First Minister Alex Salmond has rebuffed Treasury demands for Scottish ministers to withdraw their threat to renege on UK debt if they cannot secure a currency union.

Chief Secretary to the Treasury Danny Alexander has written to the Scottish Government urging its ministers to roll back on its "bogus" debt threat.

The Highland Liberal Democrat's party leader in Scotland, Willie Rennie, said a decision to "default" on debt "would trash our reputation across the globe".

Mr Salmond said he will "certainly not" withdraw, insisting Scotland cannot default on a debt it is not legally liable for and would have no moral obligation to pay without a share of Bank of England assets.

In a letter to Scottish Finance Secretary John Swinney, Mr Alexander said: "This week you have confirmed your position that the first economic policy of an independent Scotland would be to renege on the debts that have over generations funded public services and built schools, hospitals and more in Scotland.

"This is an extraordinary position and perhaps the most irresponsible claim of your entire campaign. I am writing to ask that you withdraw it - this is for the benefit of all Scots, who do not deserve to pay for your grandstanding.

"Both our governments have long accepted that in the event of a vote for independence there will be a negotiation of assets and liabilities."

He added: "Your claim that because the UK Government will not agree a currency union, an independent Scotland should not take a share of the debt is completely bogus.

"A currency is not an asset, as you claim, it is the monetary system of a state. The pound sterling will be - legally - the monetary system of the continuing UK if Scotland votes to separate."

Mr Salmond told BBC Sunday Politics Scotland: "You can't have a default when we already know as a matter of fact that there is no default, because the contractual legal liability lies with the UK Government.

"But can I just come on to the moral aspect of this. We're putting forward an argument that we should share assets and liabilities, which is a wholly responsible position.

"Danny Alexander is suggesting, because he can't stop us using the pound, that he is going to stop us having access to the financial assets of the Bank of England, nationalised in 1946, the state assets which hold the gold reserves that Gordon Brown didn't sell off, the foreign currency reserves, and also crucially at this point 27% of the gilts that have been issued under quantitative easing.

"Clearly, if Danny Alexander wants to take all of the assets then he gets stuck with all of the liabilities, which is why our reasonable position is much better."

Mr Rennie dismissed the claim that walking away from UK debt would not amount to a default.

"Crawford Beveridge (chair of the Scottish Government's Council of Economic Advisers) set out quite clearly that if it smells like a default and it looks like a default then its a default," Mr Rennie said.

"If on the first day of independence you were to walk away from a fair share of debt, that would trash our reputation across the globe."

Mr Salmond has been under sustained pressure to reveal his "Plan B" on currency if Westminster follows through on its pledge to refuse a currency union.

Mr Rennie declined to reveal what his own preferred currency would be if Scotland votes Yes, insisting he "would be loathe to pick from a range of terrible options".

He said: "If you look at the options that would be presented to the people of Scotland after independence, they would be quite draconian and would have impacts on transaction costs for business, you would have impacts in terms of being able to control the levers of the economy, to a separate country. These would be quite dramatic."