Green MSPs will only back the minority SNP government's budget plans if ministers adopt a "more progressive approach" to taxation, Finance Secretary Derek Mackay has been told.

The votes of Holyrood's six Green MSPs were crucial in passing the Budget Bill last year, and with Mr Mackay currently preparing tax and spending plans for 2018-19 Scottish Green co-convener Patrick Harvie made clear an income tax increase for higher earners must be part of that.

Mr Harvie said any budget proposal in which MSPs, who have a salary of £61,778, did not end up paying more tax would be "inadequate".

He spoke out as he addressed his party's Scottish conference in Edinburgh, telling activists there that they had been instrumental in bringing about changes in Scottish politics on issues ranging from fracking to smacking - with the Scottish Government now giving its support to a Green bill that will make Scotland the first part of the UK to outlaw the physical punishment of children.

Mr Harvie, a Glasgow MSP, also insisted the issue of public sector pay would be crucial in the forthcoming Scottish budget.

SNP ministers have already committed to ending the 1% pay cap on public sector workers - but Mr Harvie demanded they go further than this and give workers a pay rise above the rate of inflation, which currently stands at 3%.

Mr Harvie told the conference: "Public sector pay is going to be one of the most important issues in the budget discussions,

"And there is now an unanswerable case for an above inflation pay settlement for people delivering public services. I think we can win that, I think we can achieve that.

"The Scottish Government has said they will lift the pay cap, that's a good start. But simply lifting the cap isn't enough, we need to recognise higher inflation means we now have to go above and beyond that figure, and it has to be fully funded.

"If the Scottish Government lifts the pay cap but doesn't provide the rest of the public sector with the resources that are necessary then it will make very little difference, so it has to be funded and it has to be above inflation."

On the issue of taxation he said the core principles of the Greens' approach were "very, very clear", stating: "We want to raise enough revenues to fund the public services and the investment that our country needs and we want to do it in a way that closes the inequality gap instead of hitting low earners in the pocket.

"That means we need a better approach to progressive taxation. We'll be absolutely advocating for that and I am really pleased movement is happening on that as well."

First Minister Nicola Sturgeon has already signalled she wants a discussion on the "responsible and progressive" use of Holyrood's income tax powers.

And Mr Harvie said: "We need fairer, genuinely more progressive taxation and if I'm not paying more tax, if MSPs aren't paying more tax by the end of it I think that will be an inadequate settlement.

"We need to ensure that we protect low earners and ensure that those who genuinely can afford to pay more do so.

"So the message to Derek Mackay as he prepares his budget is very clear - if you want Green support these are the areas where you are going to listen and you are going to have to act."

In his speech Mr Harvie welcomed that the Finance Secretary will not be cutting Air Passenger Duty this year, as the Scottish Government have previously pledged to do.

But he insisted there was "no substantive case" for reducing the levy on air travel, and said: "I want that policy not only paused but scrapped altogether."

Mr Harvie argued: "In terms of the simple transport priorities most people know that we would be far better off if they made public transport affordable, reliable and convenient rather than cutting taxes for the aviation industry."

He highlighted a host of areas where he claimed the Greens had influenced Scottish Government policies - such as Ms Sturgeon's announcement earlier this month on the establishment of a publicly-owned, not-for-profit energy company to sell gas and electricity to customers at "as close to cost price as possible".

Ministers are also set to phase out the sale of conventional petrol and diesel cares from 2032, earlier than Westminster's target, and will start setting up low emission zones in cites from next year.

The Scottish Government has also acted to rule out fracking north of the border - though the Greens are pressing them to go further on this area, with Mr Harvie urging the SNP to "lock that in for the future".

Mr Harvie said: "The progress that we have seen for Green ideas in Scotland I believe fully justifies the title of our conference, and shows we are leading the change in Scottish politics.

"The list of Green achievements is long and getting longer. We're seeing action on polluting vehicles to improve the air quality in our cities, we're seeing the creation of a deposit return scheme that Greens have pushed for a long time.

"And with a fracking ban to the recent announcement of a publicly owned energy company in Scotland, it's clear that the positive, constructive Green policies that we have been pushing for years are making real progress.

But he also said the SNP "are not the only ones who have been inspired by Green ideas", insisting the party was having an impact "across the political spectrum".

The Conservatives are looking at a Green policy about making land available to councils at its existing use value, which would help cut the cost of building housing,Mr Harvie said.

He also said Labour had "lifted" ideas such using newly devolved welfare powers to top up child benefit payments.

With Scottish Labour in the process of choosing its latest leader, with MSPs Anas Sarwar and Richard Leonard running to replace Kezia Dugdale, the Green co-convener hit out: "I think they will continue to be in need of fresh new ideas regardless of whether their leadership election is won by the centrist dad or the one no-one's heard of."