THE UK Treasury has been accused of running a "political dirty tricks department" spinning against Scottish independence after it emerged sensitive information about Royal Bank of Scotland plans to leave the country in the event of a Yes vote was leaked by a civil servant in charge of "referendum communications" within the department.

The email, sent to journalists the week before the referendum, stated RBS had plans to move its base to London in the event of independence, triggering headlines viewed as a blow to the Yes campaign. It was issued while the RBS board was meeting to discuss the matter, and before the bank had made a statement to the financial markets - a breach of trading rules.

First Minister Alex Salmond demanded a criminal investigation into the matter, while Edinburgh financier and Independent Midlothian councillor Peter de Vink, an RBS shareholder, also asked the Financial Conduct Authority (FCA) and police to investigate.

The Sunday Herald has now obtained a copy of the email, which shows it was sent by a civil servant who is head of Scottish Referendum Communications at the Treasury.

City of London Police are also now probing the complaint by de Vink and are in the process of contacting "relevant individuals and organisations".

SNP Treasury spokesman Stewart Hosie MP yesterday said the fact the email had been sent by the head of Scottish Referendum Communications was an "extraordinary revelation".

He said: "The previous claims by the Cabinet Secretary [Sir Jeremy Heywood] that the Treasury was 'promoting financial stability' in revealing RBS plans has been totally blown apart by the revelation that it was actually a pro-active email from an official in a so-called 'Scottish referendum unit' and released while the RBS board was actually in session.

"It seems that the London Treasury had a political dirty tricks department operating throughout the referendum campaign. However, the huge problem they now face is the increasing likelihood that this particular trick was not just dirty but illegal."

Hosie added: "I will now table a series of Parliamentary questions on this issue to add to the proper and comprehensive investigations which must now take place."

The Treasury email was sent to journalists at 10.16pm on September 10, around 25 minutes before the RBS board meeting on the issue had finished. It contained a response to a statement issued by Lloyds Banking Group which stated it had contingency plans to establish "new legal entities" in England in the event of a Yes vote.

But it also gave a quote from a "Treasury source" which said: "As you would expect, RBS have also been in touch with us and have similar plans to base themselves in London."

The following day, RBS issued a statement to the markets which confirmed its intention to "redomicile" in the event of a Yes vote, but added it would intend to retain a "significant level of its operations and employment in Scotland".

RBS chief Ross McEwan also issued a letter to staff in the morning saying the business was based in Scotland because of the "skills and knowledge of our people, and the sound business environment". It added: "So far, I see no reason why this would change should we implement our contingency plans ... I know many of you will have already heard about this first in the media. My apologies for that, on this occasion this was unavoidable."

Heywood, head of the civil service, subsequently rejected demands by Salmond that the matter be investigated. He stated the Treasury email had been issued following a newspaper report, which quoted an RBS source as stating that the bank would follow Lloyds in its plans to move its registered HQ out of Scotland in the event of a Yes vote.

In a response to Salmond, he claimed it was "simply a confirmation of the Treasury's understanding of RBS' contingency planning". He added: "The Treasury judged that it was important to set this out - at a time when the UK financial markets were closed - given their overarching responsibility for maintaining financial stability in the UK."

Salmond subsequently wrote to the head of the FCA, the Chief Constable of Police Scotland, and the Commissioner of Police for the City of London urging action over the alleged leaking of market-sensitive information.

He stated the grounds for his belief a criminal offence may have been committed, including: that decisions of such a substantial nature should be a matter for the bank to report "openly and transparently" to markets; and that there had been improper disclosure of market-sensitive information, which is "tantamount to insider dealing".

He also raised concerns the action by the Treasury would have potentially created uncertainty if its information had differed from the position taken by the RBS board when its meeting had concluded.

De Vink, who filed complaints on the potential leaking of market sensitive information two days after the Treasury email was sent, said he has now been contacted by City of London Police and invited to attend an interview next month.

He said: "They have asked would you come in and talk to us, which is what I am going to do in November.

"I told them while it is a political issue, that doesn't take away that what happened was absolutely unacceptable."

De Vink also criticised the FCA for a lack of response, describing its attitude as "lackadaisical".

"I find it incredible that these things are allowed to happen," he added. "If anyone else would have done that they would have had the book thrown at them and quite understandably."

The Sunday Herald asked the FCA if the complaints were being investigated. A spokeswoman said it was unable to comment on individual complaints.

A spokesman for City of London Police confirmed it had received the letter from de Vink and added: "We are now speaking to the relevant individuals and organisations."

The Treasury claimed the person who sent the email was a "junior civil servant", despite his position as head of Scottish Referendum Communications. In a previous role he was press officer to former financial secretary to the Treasury, Greg Clark.

The Treasury also refused to give any details of who approved the email being sent out.

Last night, a spokesman for the Treasury said: "As is a matter of public record, the Cabinet Secretary has written to the former [sic] First Minister on this matter, and rejected any suggestion of improper actions by civil servants."