SIR Nicholas Macpherson, the former permanent secretary to the Treasury who clashed with Alex Salmond during the independence referendum campaign, has claimed Brexit means Scotland leaving the UK now would present it with an “an extraordinary opportunity” to attract skills and investment.

In an extraordinary column in The Financial Times, Sir Nicholas says the UK’s decision to leave Europe “changes terms of debate north of the Border” and that Scotland could “develop further as a financial centre”.

He writes: “With the UK leaving the EU, there is a golden opportunity for proponents of Scottish independence to re-appraise their economic prospectus. Clearly, membership of the EU will lie at the heart of it.

"That will enable Scotland to have access to the biggest market in the world without the uncertainties that are likely to face the rest of the UK for many years to come. It would also provide a historic opportunity for Edinburgh to develop further as a financial centre, as London-based institutions hedge their bets on the location of staff and activities.

Sir Nicholas goes on to say: “An independent Scotland committed to the EU would have an extraordinary opportunity to attract inward investment as well as highly skilled migrants.

“If it can develop a clear and coherent economic strategy ahead of any future referendum, it not only stands a better chance of winning, it will also increase the probability that an independent Scotland inside the EU can hit the ground running.”

On currency, he says there should be a Scottish pound supported by a central bank, rather than an attempted currency union with the remainder of the UK.

He says that, despite resistance from Spain worried about Catalonia, the EU would have a “huge interest in fast-tracking membership for a country whose citizens have been members of the bloc for 43 years and have voted to remain by 62 per cent to 38 per cent.”

And though this would “almost certainly” mean Scotland having to adopt the euro, he points to the Swedish example, where it is more of a theoretical position. Sweden has been committed to joining the euro for 20 years, and “the prospects of its giving up the krona seem vanishingly remote,” Sir Nicholas writes.

This Scottish currency would allow Scotland to manage its volatile oil price cycle, he says: “The Treasury was concerned in 2014 that the Scottish Government’s prospectus relied on over-optimistic oil price projections. But First Minister

Nicola Sturgeon’s administration has since worked to bolster its fiscal credibility.”

Reacting to the article on Twitter, the First Minister said: “This from Nicholas Macpherson, the chief architect of the Treasury’s anti-Indy stance in 2014, is quite something.”

Sir Nicholas was criticised by the SNP and Yes campaigners for publishing his advice to Treasury ministers warning against a currency union with Scotland in February 2014.

That criticism was later supported by a cross-party committee of MPs looking into the role of the civil service in the Scottish independence referendum campaign.

The Public Affairs Select Committee said the Treasury mandarin had risked the Civil Service’s reputation for impartiality.

They dismissed his defence that the independence referendum was an exceptional case where the “very existence of the British state was at stake”.

Their report said: “The only purpose [for releasing his letter] was to use the impartial status of a permanent secretary to give authority to the advocacy of a political argument.”