THE SNP’s plan for a new currency in an independent Scotland has come under fire after the party’s Westminster leader said it would be pegged in value to sterling.

Ian Blackford said the new currency would shadow the pound, implying Scottish Central Bank reserves of up to £300bn built up over many years.

READ MORE: SNP says it would tie new currency to the pound

It would also mean tying a Scottish pound to sterling’s exchange rate, giving the Bank of England continued significant control over Scotland’s economy.

Critics said the plan would squeeze public spending, as huge sums would have to be diverted into reserves to stop speculators trying to knock the currency off its peg.

SNP activists last month defied Nicola Sturgeon to adopt a new party policy of switching to an independent currency “as soon as practicable” after a Yes vote, subject to six tests.

However, they explicitly rejected a proposal to peg the currency initially to the pound.

Ms Sturgeon this week suggested the euro might be a “perfectly sensible” option as well after her MEP Alyn Smith said he was “agnostic” about which currency was used.

SNP policy in 2014 was to share the pound indefinitely with the rest of the UK.

Until now, the SNP has not said if a new Scottish currency would be free-floating - and liable to devaluation - or would aim to hold its value by fixing, or pegging, to the pound.

But speaking on LBC radio, Mr Blackford, a former banker, said it would be pegged to sterling to address voter fears over their savings and pensions losing their value.

He said: “We will have a series of economic tests which the Central Bank will validate when the time comes, as appropriate, to establish our own currency.

“But one of the things I would state - and this is really important, is that when we do that, one of the key items will be making sure we have sufficient reserves, because when we do have our own currency it has to be pegged against the pound sterling because we need to make sure that - savers, pensioners - that their interests are protected, and that is the reason we’ll do that on that that basis.”

READ MORE: Top SNP candidate 'open to an independent Scotland joining the euro' 

The Highland MP's remarks chime with the SNP’s Growth Commission, its economic blueprint for an independent Scotland, which said: “In the event of a new Scottish currency being created it is likely that a period of 1:1 pegging with sterling would make sense for the short and possibly medium term.”

However, the idea of taking years to build up reserves for a pegged currency is likely to anger the Left of the Yes movement, who want to ditch the pound as soon as possible.

Economist Professor Ronald MacDonald of Glasgow University’s Adam Smith Business School has previously said pegging a Scottish currency to sterling could require £300bn in reserves to protect it from economic shocks and speculators, ten times the £30bn in reserves required for a free-floating currency.

Former Labour MP Pamela Nash, chief executive of the anti-independence group Scotland in Union, said: “The SNP’s currency plan is in utter chaos. This would be catastrophic for Scotland’s economy as it would require billions of pounds in reserves, leading to devastating cuts to public services, higher borrowing and drastic tax rises.”

An SNP spokesperson said: “one-to-one pegging with sterling would make sense for the short and possibly medium term”.