The Scottish government is to ask the Chancellor for a £2billion advance to pay for the new Forth crossing, casting doubt on the SNP's controversial Scottish Futures Trust public funding scheme whch was to replace the Private Finance Initiative north of the Border.

Ministers were accused by the Opposition yesterday of trying to avoid embarrassment over their much vaunted, but never-used, futures trust (SFT), by asking Alistair Darling to front-load the Scottish budget during the bridge's construction and recoup the cash during the 20-years after its completion.

Stewart Stevenson, the SNP transport minister, also announced that work on the new bridge will begin in 2011 with a completion date of 2016. Once the new bridge is built, the existing Forth Road Bridge will continue to be used for public transport, pedestrians and cyclists. All cars and lorries will use the new crossing.

The new structure will be narrower than originally planned with two lanes either way. The estimated cost will be between £1.7billion and £2.3billion - nearly £1.7 billion less than the original estimate of up to £4billion.

The announcement was the main focus of Mr Stevenson's Strategic Transport Review - a list of 29 priority transport projects in Scotland between now and 2028 costing an estimated £12billion.

SNP ministers believe that Mr Darling will have no option but to agree to the cash advance for the crossing although the Chancellor could question the arrangement.

As well as baulking at the 20-year repayment period suggested by the Nationalists, Labour sources said that Mr Darling may well tell the SNP government that an accepted funding mechanism is already available in the shape of PFI. But this is a risk for Labour in Scotland since the Nationalists will accuse him of risking other big public sector building projects.

John Swinney, the SNP Finance Secretary, told journalists that if Mr Darling did not agree, the money for the bridge would have to come from the Scottish government's £3.5 billion capital budget, to the detriment of schools, hospitals and new roads.

Yesterday's announcement by the SNP raised questions over the future of the SFT. Opposition parties said that the absence of SFT involvement in Scotland's biggest-ever public construction project was an admission that it was not “fit for purpose” and would be dumped.

Mr Stevenson said that the proposal for the new crossing did not mean that the Treasury was paying for it, “but it would mean ... capital budgets in later years would be correspondingly reduced”.

The new Forth crossing would be publicly funded through a conventional design-and-build contract. “This delivers the best value for money and the certainty of delivering the replacement crossing by 2016,” Mr Stevenson added. However, conventional public sector projects are notorious for going over budget and for delays, with the Scottish Parliament building a prime example. Mr Swinney said he was adamant that this would not happen with the new bridge.

Scottish ministers approved the new crossing in principle a year ago after corrosion in the current bridge led to fears that it might close to lorries by 2013. Engineers say that efforts to arrest the corrosion were successful and the bridge could carry present levels of traffic until 2017, possibly 2021.

Many of the other projects outlined to MSPs yesterday - described as a “wish list” by Labour - are aimed at improving transport links, including increasing rail services between Glasgow and Edinburgh to 13 an hour by 2016 and reducing the journey time between the cities to 35 minutes.

A train station is to be built on the Fife rail line near The Gyle on the outskirts of Edinburgh, linking with the Edinburgh tram network and Edinburgh Airport. The programme also includes the intention to improve the A9 to dual carriageway standard between Perth and Inverness. The A96 Inverness to Aberdeen road would be upgraded to a dual carriageway between Inverness and Nairn.

There are also plans for faster and more frequent rail services between Inverness and Glasgow and Edinburgh, cutting journey times by up to 30 minutes.

Des McNulty, the Labour transport spokesman, described the project as a “cruel con” with many projects destined never to be delivered.

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