A cross-party group of politicians and an independent MSP joined forces yesterday to back the provision of trams in Edinburgh.

Councillors and MSPs from the Labour Party, the Liberal Democrats, the Greens and the Conservatives, as well as Independent MSP Margo MacDonald, are backing proposals for trams in Edinburgh, which are under threat from the SNP administration.

Campaigners, working under the banner Don't Trash Our Trams, said with work already begun on the tram system, cancelling it now would cost more than £100m - with nothing to show for it.

They insist cancelling the project would mean there were no viable solutions to Edinburgh's growing congestion problem, or of providing an efficient, mass-transit public transport system.

Scotland would then join Luxembourg, Cyprus and Malta as western Europe's only countries whose capital cities do not have a rapid transit public transport system.

However, First Minister Alex Salmond has raised concerns about the tram scheme. He said the remainder of the money to complete the £592m project could be put to better use elsewhere, and questioned why there had been little physical sign of progress.

Mark Sydenham, of Friends of the Earth Edinburgh, said: "A lot of work has gone into the tram system and there is clearly massive public support for the scheme. There are no alternatives to Edinburgh's congestion problem other than a modern tram system for our capital city."

Those supporting trams include Mark McInnes, the city council's Tory transport spokesman, Maggie Chapman, Green Party councillor, Robin Harper, Green MSP, Ricky Henderson, Labour's transport spokesman for the city, Ewan Aitken, leader of the Labour councillors in Edinburgh, and Margaret Smith, LibDem MSP.

Mr Aitken said: "To cancel trams would be an attack on Edinburgh and as a consequence an attack on Scotland and the Scottish economy.

"To remove the investment in trams and say you can replace it with buses is fairyland politics. There are 50 buses an hour in Princes Street at the moment. The maximum you could get would be 60, but you would need 120 buses to carry the same number of passengers as trams."

Mr Harper said: "This is part of the necessary move to a low carbon economy and delivering viable alternatives to the private car. That is what the frustrated motorist sitting in a traffic jam wants, and that's what we want."

Edinburgh Chamber of Commerce said an online poll among its members, including 1700 companies with 100,000 employees, showed 75% were in favour of the project.

Ross Laird, chairman of the chamber of commerce, said: "Our members are deeply concerned about congestion in Edinburgh, which is worsening year by year. This is already hitting businesses. Our transport group has consistently taken the view that the project will inject momentum into the economy of Edinburgh and Scotland."

Mr McInnes said the tram system would be an "enormous" benefit to the infrastructure of Edinburgh while Ms McDonald is also in favour, despite conceding the scheme would bring disruption during its construction.

She added: "I have concluded we should bite the bullet and join all the other European cities which have successfully introduced trams."