THE civil service has been dealt a stark warning to remain impartial in any future independence referendum in a damning report which criticised actions taken by both the UK and Scottish governments ahead of last year's vote.

A committee of MPs said that David Cameron's administration should not have published a controversial warning by the Permanent Secretary to the Treasury against sharing the pound with an independent Scotland.

The advice was made public only "because it suited UK ministers' political objectives" in the fight for a No vote and the move compromised the perceived impartiality of one of the UK's top civil servants, MPs found.

The report by the Commons Public Administration Select Committee also hit out at the Scottish Government's White Paper on independence, saying it did not meet the "factual standards" expected.

MPs said Scottish ministers' 670-page blueprint for independence "raised questions about the use of public money for partisan purposes", criticising the fact it included pledges the SNP could implement only if the party won the 2016 Holyrood election.

Among its recommendations, the report calls for the Civil Service Code to be "revised to specifically refer to referendums and provide civil servants across the UK with clear and definitive guidance on their role in respect of referendum campaigns".

The criticisms could also have ramifications for the In/Out vote on the UK's membership of the European Union which the Conservatives have promised to hold in 2017 if they win a majority in May's General Election.

Bernard Jenkin, the Conservative MP who chairs the committee, said: "The Scottish independence referendum created exceptional circumstances, but that does not make it acceptable for parts of the civil service to approve the use of public funds to promote the agenda of one political party, to become personally aligned with one side or the other in the referendum debate.

"Referendums currently get no mention at all in the Civil Service Code. We suggest a limited change to the Civil Service Code to address referendums that will remove ambiguity about this."

The Treasury defended the decision to publish the warning by its top civil servant Sir Nicholas MacPherson to the Chancellor George Osborne, saying that the independence referendum had been an "exceptional case".

In the letter Sir Nicholas warned that a currency union between a separate Scotland and the rest of the UK would be "fraught with difficulty".

Just days later Mr Osborne publicly announced his government's opposition to any formal deal to share the pound.

The Commons Public Administration Select Committee said that the publication of the Treasury advice had "compromised the perceived impartiality of one of the UK's most senior civil servants".

The MPs call on the Prime Minister make it clear "that the publication of advice to ministers will never recur".

On the White Paper the report warned it "included a description of the SNP's proposed programme for government that was contingent upon their winning the 2016 Scottish Parliament elections".

"This did not uphold the factual standards expected of a UK Government White Paper and therefore raised questions about the use of public money for partisan purposes," it said.

The report said that mandarins should "not be required to carry out ministers' wishes, if they are being asked to use public funds to promote the agenda of a political party, as was evident in this case".

Sir Nicholas told the committee it was "highly unusual" for his advice to be made public.

But he defended the decision, which he said had been taken in a bid to reassure the markets.

MPs rejected that explanation, saying: "The advice should not have been published. Its publication compromised the perceived impartiality of one of the UK's most senior civil servants."

The committee has now recommended that guidance regarding the publication of advice from civil servants "should be reiterated and if necessary revised to ensure that a civil servant's advice to a minister cannot be published in future, in order to protect the impartiality of the civil service".

A spokesman for the Treasury said: "As we have made clear before, the question of whether or not the UK would agree to a currency union was an exceptional case where it was important that the arguments were exposed in full before a referendum rather than after it."

SNP Westminster Leader Angus Robertson said: "We knew the Treasury failed to act in accordance with civil service impartiality rules and this report sets outs the steps which must be taken to ensure such a breach does not happen again.

"We expect the highest standards from senior civil servants and Sir Nicholas MacPherson and the Treasury fell short."

Scottish Labour, meanwhile, said the White Paper was a "taxpayer-funded manifesto for the SNP, not a constitutional blueprint".

"The SNP government must reassure the people of Scotland that they will take heed of this report and stop interfering with the civil service," a spokesman said.

A Scottish Government spokesman said the White Paper, Scotland's Future, met the "highest professional standards" and was a "proper use of public funds".

He added "The Scottish and UK Governments have frequently set out policy intentions whose implementation depends on the outcome of future elections. Indeed, just last week, the UK Government budget set out a range of policies of the governing parties where implementation will fall beyond the general election.

"Scotland's Future reflects not only the powers that would come to Scotland under independence, but how they could be used in a real and practical way. The document makes clear the distinction between these two types of proposal."