A £2.34 billion plan for a new Forth Bridge has been thrown into doubt after the Chancellor refused to advance funding for the project.
Alistair Darling ruled out the idea, saying it was impossible to bring forward money that had yet to be allocated.
But First Minister Alex Salmond insisted the Scottish Government would not take no for an answer on the subject.
The Scottish Government has unveiled 29 different transport proposals, including the new Forth Bridge.
Scottish ministers hoped the Treasury would agree to bring forward money due to the Holyrood administration over a number of years to pay for the crossing.
But speaking on BBC Radio Scotland's The Business programme, the Chancellor insisted: "What you can't do is to bring forward spending from a budget that hasn't yet been allocated in 15 or 20 years' time."
Finance secretary John Swinney said that if the Treasury did not agree to bring forward cash to help fund the new Forth Bridge, Holyrood ministers would "simply have to make choices" about their capital programme.
Mr Darling, the MP for Edinburgh South West, said there was "complete agreement" on the need for a second Forth crossing.
And he said the Treasury was "happy to work with the Scottish Government, to co-operate closely and to find a solution".
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