THERE is a saying in Glasgow that you should always look up: guaranteed there will be some architectural gem to please the eye.

But imagine a very different urban landscape, one where Central Station, George Square and the Merchant City no longer exist and the distinctive styles of Charles Rennie Mackintosh and Alexander "Greek" Thomson have been erased.

A new BBC programme is set to unveil the futuristic metropolis Glasgow might have become had the vision of a leading architect been realised.

Dreaming the Impossible: Unbuilt Britain, which begins on BBC Four tonight, will outline radical 1940s council-backed plans to demolish the entire city and start over again from scratch.

Using computer generated images it depicts the uniform rows of high rise apartment towers and office buildings which could have risen from the ashes.

Made for the BBC by Timeline Films and presented by architectural historian Dr Olivia Horsfall Turner, the three-part series examines British building projects that never made it off the drawing board.

Glasgow will feature in the third episode to be broadcast a fortnight tonight which documents an ambitious proposal following the Second World War.

With much of the city's housing stock dilapidated and decaying, the Glasgow Corporation charged its chief engineer Robert Bruce as the man to solve the crisis. The Bruce Report was published in 1945.

"It's hard to explain this report without sounding melodramatic but that's because his plan was quite staggering," said Dr Horsfall Turner. "Bruce proposed demolishing Glasgow's Victorian city centre and starting all over again.

"He didn't want to just demolish the slums: he wanted to get rid of everything. Casualties would have included Glasgow School of Art by Charles Rennie Mackintosh, Central Station and the buildings of Alexander "Greek" Thomson.

"In his report he stated that re-planning should be 'surgical' and that 'boldness' is required," she added. "Bruce's description of performing surgery on the city feels like something of an understatement when one looks at the plans that he devised. This just wasn't a face lift: it was a complete heart transplant."

But not everyone shared his vision and among its most formidable opponents was Sir Patrick Abercrombie, one of the 20th century's most famous urban planners, who was given the high profile task of re-building London after the Second World War.

"His solution to the capital's problem of overcrowding had been to propose new towns, smaller satellite communities that would syphon off the excess population from London," said Dr Horsfall Turner.

Asked by the government to turn his attention to Scotland's biggest city, in 1946 Abercrombie published a rival report to Bruce's called the Clyde Valley Regional Plan. He emphatically concluded that the solution to overcrowding in Glasgow was for half the population to be dispersed to new towns.

But Glasgow Corporation, keen to maintain its status as second city of the empire and fearful a mass exodus would dilute this, instead backed Bruce, formally approving his scheme in 1947.

Then, two years later, came a dramatic U-turn. "The investment required for the scale of rebuilding, particularly at this point in time, would have been astronomical," said Dr Horsfall Turner.

Today, there are few who would rue the fact it never came to fruition, as Glasgow would have lost much of its character and beauty.

"While Bruce's vision was clean, efficient, inspiring and spoke of the future, security and equality, the aesthetic of that was so uncompromising and stark," said Dr Horsfall Turner. "It's very difficult to imagine the multiple connected families, living cheek by jowl in the Glasgow tenements, suddenly being transposed to a very different kind of architectural regime.

"Buildings are containers for living, but there is something much softer in what we need from them. They inform the way that human beings build social relations. To think of those families, who were living in tenements, being put into high rise flats is devastating really."

The series also examines plans in the run-up to the First World War to build a sea canal through the heart of Scotland, allowing Naval battleships to cross from west to east.

Two schemes were proposed for the Mid Scotland Ship Canal, the first mooted to run from the Clyde estuary, via Loch Lomond, to the North Sea. Equal in size and scale to Panama Canal, the price tag was £8 million - the equivalent today of £2.7 billion.

The second, almost 20 miles shorter, was to link the Clyde with the Firth of Forth, creating a new waterway through central Scotland alongside its existing canals.

But the project was deemed too expensive. Dr Horsfall Turner believes that had the Mid Scotland Ship Canal come to pass, it could have led to lasting economic benefits today.

"Although it would have been radical in terms of what it would have done to the Highland area of Scotland, effectively creating an offshore island, the potential for commerce, trade and continuing shipbuilding along the Clyde would have been greatly enhanced," she said. "It would probably, by now, have created a fantastic cruise liner destination and is interesting to think how it might have affected the ongoing viability of the country's shipyards."

l Dreaming the Impossible: Unbuilt Britain starts tonight on BBC Four at 9pm