T party: Strathallan Castle owner Anna Roberts and T in the Park founder Geoff Ellis discuss the festival's new venue

Just up ahead, nestling amid the verdure, is the imposing 19th-century baronial castle itself, complete with Saltire flying from the ramparts.

As I approach the huge wooden door I turn and survey the tranquil parkland beyond: can it be true that in just a few days' time this landscape will become the nation's fifth biggest city? It certainly can. Strathallan, just outside Auchterarder, is the new home of T in the Park.

Next weekend some 85,000 music fans will descend upon the estate to experience the latest incarnation of Scotland's biggest music festival, which has been forced to move from Balado after 18 years at the Kinross-shire site, due to safety concerns over an old pipeline.

Following a protracted battle over planning permission, the transformation of Strathallan from country estate to festival site is now well underway. On the day I visit, the main stage, which will be headlined by Kasabian, Swedish DJ Avicii and Noel Gallagher, is being constructed just below the castle and large teams of contractors are installing the final pieces of infrastructure that will support the mammoth event, now in its 22nd year.

It's the start of a new era for both the festival, run by DF Concerts, and Strathallan, which has been owned by the Roberts family for a century. The castle, still a family home, already hosts weddings and corporate events. It also has a history of flexibility: during the First World War it served as a military hospital, while in the Second it hosted evacuated girls from Glasgow's Laurel Bank School.

But welcoming 85,000 21st-century music fans on to your land is, one would imagine, a whole different ball game.

Anna Roberts, who owns the castle and co-owns the estate, seems surprisingly relaxed at the prospect.

"We were approached by DF about hosting the festival a couple of years ago and to be honest it wasn't a hard decision," says the 41-year-old over coffee in the castle's chilly library, speaking to the media for the first time.

"It's been a hard route for DF but the company's track record over the last 18 years at Balado speaks for itself. It was a no-brainer."

Quietly spoken and dressed in down-to-earth jeans and fleece, Roberts is the fifth generation of her family to own Strathallan and the first woman to run it. She grew up in the castle - and still lives there - taking over the running of the building and much of the attached 1,000-acre estate following the death of her father, Sir William Roberts, in 2012.

An agriculture graduate, she says her aeroplane-enthusiast father was "open-minded", hence the castle passing to her rather than being automatically inherited by her elder brother Jamie, who owns land on the estate and runs a livestock farm. Another brother and two sisters live in the area too.

Roberts is realistic about the challenges facing big estates like Strathallan in the modern world. The days of Downton-esque privilege and privacy are long gone.

"T in the Park has put us on the map," she says. "It allows us to reinvest in the estate and look at doing restoration work on the house.

"A hundred years ago there were probably 85 big houses in Perthshire - very few of those still exist. Strathallan is liveable, of course, but the maintenance costs are becoming prohibitive and top-heavy. Agriculture doesn't sustain an estate like this any more, that's why you have to look to other opportunities."

She points to nearby estates such as Blair Castle, which runs a full range of outdoor activities for visitors and has its own holiday homes and caravan park, and Scone Palace, which plays host to the Rewind music festival.

"My ultimate aim is to hand it on to the next generation in better condition than I got it," adds Roberts. "That's what T in the Park gives us the chance to achieve."

It was a golden opportunity, however, that looked until recently like it might not happen at all, as the planning permission process dragged on and a series of significant hurdles got in the way. Following the announcement of Strathallan as the preferred T in the Park venue, a small but vocal and organised local campaign group was set up to oppose the festival on environmental grounds.

The Woodland Trust added its voice to the opposition, which was compounded earlier this year by the arrival of a pair of breeding ospreys, meaning a costly full planning application would have to be submitted. Perth and Kinross Council, which had licensed the festival for 18 years at Balado, ordered lengthy public consultations.

A jittery few months followed, as festival organisers worked with organisations including the RSPB, Scottish National Heritage and Sepa to assuage archaeological and environmental concerns and ensure adequate protection for the nesting ospreys and other wildlife.

Just weeks before the multi-million pound festival was due to take place, planning permission was finally granted by the council for a three-year period, during which the environmental impact will be assessed.

DF chief executive Geoff Ellis, who joins us in Strathallan's library, admits the last year has been the hardest in T in the Park's 22-year history, but says bringing the festival here has been worth the pain - which includes the "seven-figure" cost of installing infrastructure - as the event now has a secure long-term future. Both he and Roberts see this as a permanent home for T in the Park.

Ellis, a 50-year-old Mancunian and a familiar face on the Glasgow music scene for more than 20 years, has grown the festival from a two-day, 20,000 capacity event at Strathclyde Park, just outside Glasgow, to its current position as one of the biggest and most respected music festivals in Europe.

Recent years at the Balado site have seen an eclectic list of headliners including Beyonce, the Foo Fighters, The Arctic Monkeys, The Pixies, Rhianna, The Stone Roses and Pharrell Williams.

Surely at some point Ellis must have thought the whole game was a bogey? The stakes were certainly pretty high. Finding another site for the festival at short notice was never going to be a viable option, and staging the event costs, according to DF, another "seven-figure sum" regardless of where it takes place. A recent independent report into the value of music tourism in the UK found that T in the Park brings £15.4m to the Scottish economy as a whole, and £2.75m to the local area that hosts it.

Listening to Ellis describing the challenges of the last few months, I wonder if he ever thought that planning permission wouldn't be granted? His answer comes straight off the bat.

"No, never. Maybe I'm naive, but I always knew we could deliver the requirements. We had a great team of people, a visionary landowner and a council we've been working with for 18 years.

"I understand the fear of the unknown for local residents, but this wasn't a case of fear of the unknown for Perth and Kinross councillors because they've licensed us for 18 years.

"Sepa, Scottish Natural Heritage, they all know us. People could try to scare them and say we're going to kill all the wildlife, but they knew how we operated at Balado, which was a site of special scientific interest.

"We were the first festival that had to have an environmental manager and all the right accompanying policies from 1997, before it was fashionable.

"There is more wildlife here at Strathallan, of course, but we had bats at Balado and other birdlife, and osprey could have turned up at any time."

In his next life, Ellis jokes, he will be an "ologist" of some sort. He says the nesting pair of ospreys at Strathallan is probably now the most studied pair on the planet, and admits to having intimate knowledge of their behaviour, including "what time the female does the toilet in mid-air and what time the fish comes in". He gets a daily report on the birds from specialist ornithologists.

He is also adamant that the local community in Perthshire has supported the bid to bring T in the Park to their doorstep from the off.

"Look, whenever I needed any reassurance that we are doing the right thing, I would go into Auchterarder or Crieff and sit in a cafe and talk to people," he says. "People of all ages said it was a great thing. Many of them would never dream of going to T in a million years, of course, but they think it's great for the area."

Despite the stumbling blocks, the infrastructure now in place means logistics will be far easier going forward, adds Ellis. And with just a week to go to the first Strathallan T in the Park, he likens the atmosphere in the area to Glasgow in the lead up to last year's Commonwealth Games. He says shops, hotels and B&Bs are already benefiting from the contractors brought in to set up, and that local businesses will be able to look forward to a yearly return.

Before today's interview, I popped into the town for a wander and took a straw poll in a cafe and the local Co-op supermarket. Of the 10 people I spoke to, none was against holding T in the Park at Strathallan. There were concerns about traffic, but many mentioned the fact that the area had already successfully hosted the G8 summit and the Ryder Cup. They said since T in the Park is an annual event, they'll be able to plan ahead. More than one used the phrase, "no pain, no gain". Strathallan T action group, STAG, have, however, stressed that without "realistic and adequate protection" for the ospreys, "some very serious questions will be raised".

Roberts is keenly aware of local opinion. Unlike Ellis, of course, she lives here all year round. "It's a new site and we'd be naive to think we'll get everything right in year one," she explains. "But we will have the time to improve things and move forward.

"DF has been very open from the start, and they gave local people the chance to go to Balado and see how the festival is run. I went myself for the last two years.

"The nature of something like this means you're always going to get a small number of people who just don't want it. But people who are born and bred in the area, who have lived here all their lives, have embraced it and that's something I'm very proud of."

Ellis views the move to Strathallan, which he says was always on his radar as possible site, as a "whole new chapter" for the festival.

He says he looked at other sites, but many were too far north or wouldn't be able to accommodate the 85,000 daily capacity needed. Strathallan's central belt location was key, providing easy access from Glasgow, Edinburgh, Dundee and Aberdeen, the Highlands and the north of England.

He adds that although there were "a couple" of other options, the beauty of Strathallan put the site in a different league.

"I don't think the event was tired," he insists. "The demand is still there. But if you can reinvigorate something before this needs to done, that's the way to go.

"Having a blank canvas was the exciting part, putting the jigsaw together. Obviously there has been pain, but you can't just sit back."

He says the festival will naturally evolve, as tastes and sound systems change. He also sees opportunities to improve transport links and bring more people to the event from the north of England, particularly by train.

But Ellis believes the basic elements of T in the Park, the things that have made it so successful over the years, will stay the same.

"The atmosphere, the warmth and energy of the crowd, the spirit and essence of T, none of that will change," he says.

"But this year the surroundings will be like nothing music fans have seen before at a UK music festival. The beauty of this site will be the real wow factor.

"If people are in picturesque surroundings, they respect the environment more. Our surveys tells us that atmosphere comes really high in what people are looking for from T. They trust us on that one.

"This year they'll open their tent, see the woodland and look up to the castle - they'll be kings and queens for the weekend. Some said we were crazy going to so much trouble to move here. But this is the place people will want to come back to year after year."

Considering how he's taken T in the Park from strength to strength over two decades, you wouldn't bet against Ellis.

Roberts smiles when I suggest she might want to lock herself away in the castle's soundproof cellar while the festival is in full swing next weekend.

"Not at all, I'll be getting the deck chairs out," she laughs. "I'll be right in the thick of it all. I'm looking forward to seeing Noel Gallagher and Avicii."

A brief history of T

NOW one of the biggest music festivals in Europe, T in the Park started from humble beginnings at a time when music was clearly categorised by genre, Britpop was riding high and CD sales were everything.

The festival was created by Stuart Clumpas, owner of legendary Glasgow music venue King Tut's Wah Wah Hut, and Geoff Ellis, the Mancunian who came north in 1992 to be its promoter, and is now chief executive of DF Concerts, the company that still runs the event.

Taking its name from the main sponsor, Tennent's lager, the inaugural T took place at Strathclyde Park, near Motherwell, in 1994, with a crowd of 17,000. It didn't sell out.

Scotland had never seen anything like it - at the time the UK's only big festivals were Glastonbury and Reading - and the eclectic line-up included Rage Against The Machine, Primal Scream, Bjork, Teenage Fanclub, Blur, Pulp and the Manic Street Preachers.

A smaller stage showcased up-and-coming Scottish bands, which included Glass Onion, who would later headline the main stage as Travis.

A year on, tickets sold out, Noel Gallagher joined Paul Weller on stage and Kermit from the band Black Grape famously kept singing after breaking his leg. To underline its eclectic credentials, the festival introduced a dance tent.

It was during this period that T in the Park got its reputation as a particular favourite with bands, mainly thanks to the ever enthusiastic Scottish audience.

"T in the Park audiences are the most passionate in the world," says Ellis. "They are more passionate than English festival audiences, who are in turn more passionate than audiences in America. The atmosphere is everything."

By 1997, the festival had outgrown Strathclyde Park and organisers were keen that it should be a festival for the whole of Scotland, not just Glasgow.

It moved to Balado, near Kinross, where capacity increased to 45,000 a day. This eventually rose to 85,000, making T in the Park Scotland's fifth largest town, with infrastructure needs to match.

The festival stayed at Balado for 18 years, but was forced to look for a new site following safety concerns over an old pipeline. Next weekend, T in the Park will hold its first event at its new home, Strathallan Castle in Perthshire.

Since 1994, the festival industry has been transformed. The UK now has hundreds of events - many of which are held in Scotland - and going to a festival is more a rite of passage for young people than a musical statement. But T in the Park is still biggest - and arguably the best - in Scotland. Much of its audience has grown up with the event and goes year after year, regardless of who's on the bill.

"People thought we were mad and that a big music festival in Scotland would never work," says Ellis. How wrong they were.