The Scottish government has served notice that it is to press ahead with the new £2 billion Forth crossing despite growing concerns about the potential impact on the environment and the financial implications for other public sector construction projects.

Opponents of the crossing, which would be Scotland’s largest infrastructure project, claimed that repairing the existing Forth Road Bridge would be a more cost-effective option and gave warning that a new bridge would undermine the SNP government’s targets on cutting carbon emissions.

Ministers at Holyrood, who yesterday published their Forth Replacement Crossing Bill, are convinced that the new bridge is needed to safeguard the economic health of the East of Scotland.

The Bill paves the way for a new bridge to be built at a cost of between £1.7 billion and £2.3 billion. Construction is expected to start in 2011 and is due for completion in 2016. The Bill is expected to complete its parliamentary journey by the end of next year.

Although work is underway to counteract corrosion of the cables of the present road bridge, amid warnings that it could be closed to traffic in ten years, that is not seen by the government as a sustainable long-term solution.

The new bridge will include a two-lane carriageway with hard shoulders, spanning approximately 2.7km (1.6 miles). It will be a cable-stayed bridge with three “mono-towers”, two central spans of approximately 650m (2,130ft) each and approach viaducts, as well as trunk road connections north and south of the bridge.

When it opens, the existing bridge will be used only for public transport, pedestrians and cyclists.

The decision to fund the new bridge comes against a background of forecasts that the Scottish budget could decline by as much as 13 per cent in real terms by 2014.

SNP ministers failed in an attempt to convince the Treasury to allow them to pay for the bridge by raiding future capital budgets with the cash repaid over the subsequent 20 years.

Instead, the Treasury has tabled an alternative plan to let Holyrood use £500 million from Scotland’s Barnett Formula share of the London Crossrail project, £300 million from Scottish under-spending held by the Treasury and another £400 million from efficiency savings — a total of £1.2 billion. The remainder would come as it was needed from annual capital budgets.

That offer, although still on the table, has been dismissed by SNP ministers who are playing down fears that the result will be that other transport projects in Scotland will have to be cut back or put on hold to pay for the new bridge.

Alison McInnes, the Liberal Democrat transport spokeswoman, said that the proposed funding package was unacceptable and called on the government at Holyrood to sit down with the Treasury and establish a better package “for this vital bridge”.

The Scottish government’s position is that given the uncertainty of the future viability of the current bridge, the nation cannot afford any delay and that the money will be found to pay for it.

Stewart Stevenson, the Transport Minister, said: “That is why we are taking the earliest possible action to prevent serious disruption to cross-Forth traffic arising from maintenance and repair works. The economic importance of this scheme demands we get this project right.”

Meanwhile, environmental groups say that repairing the existing bridge would cost only £122 million while a new crossing will lead to additional carbon emissions, contrary to the government’s target of combating climate change.

Juliet Swann, head of campaigns at Friends of the Earth Scotland, said: “It is astonishing that ... in the run-up to the critical Copenhagen climate change talks, the largest infrastructure project in Scotland is a road bridge designed to accommodate everincreasing levels of traffic growth.”

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