WE ARE used to the tradition of senior civil servants talking in the guarded language of Sir Humphrey from Yes Minister.

Not so Sir Nicholas Macpherson, Permanent Secretary to HM Treasury, whose blunt advice to the Chancellor was released yesterday. Mr Osborne said he was taking the "exceptional step" of publishing this internal advice, and it's not difficult to see why.

Dated Tuesday of this week, the memo amounts to a devastating critique of proposals for Scotland to share sterling and the Bank of England and hints strongly at distrust of Edinburgh's ability to run its own economy.

"I would advise strongly against a currency union as currently advocated, if Scotland were to vote for independence," Sir Nicholas stated.

"To sum up, I would advise you against entering into a currency union with an independent Scotland. There is no evidence that adequate proposals or policy changes to enable the formation of a currency union could be devised, agreed and implemented by both governments in the foreseeable future."