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The Treasury briefed journalists about RBS's intention to relocate to London if Scotland were to go for independence, before RBS's board had formally made the decision to announce the move, I have learned.

In a related development, the First Minister of Scotland has accused the Treasury in a new letter to the Cabinet Secretary of a "politically motivated breach of all accepted protocols on market sensitive information", in the way that it disclosed to the media on Wednesday evening that Royal Bank of Scotland was planning to move its legal home across the border.

Alex Salmond makes the allegation in a letter to Sir Jeremy Heywood, the UK's most senior civil servant, in which he asks Sir Jeremy "which minister or official authorised the release [of the information about RBS]" and "at what time the information was released".

On the News at 10 on Wednesday September 10, my colleague Nick Robinson disclosed that Lloyds and RBS would be moving their registered offices from Scotland to London - so that they would continue to be protected and regulated by the Bank of England in the event of Scots voting for independence.

The Sun newspaper also had the story - which was perceived as embarrassing for Mr Salmond and the campaign for independence.

At 10.16pm that evening I and other journalists were emailed by the Treasury to be told that Lloyds had "issued a statement" on moving its domicile to London and that RBS had been "in touch with the Treasury" and had told the Treasury of "similar plans to base themselves in London".

I learned today that RBS's board was still meeting at this time, to decide whether to tell its shareholders the following morning at 7am that it too would move its domicile in the event of Scotland separating from the UK.

RBS's board meeting was convened for 9.45pm, it started at 10pm and finished around 11pm.

In other words, the Treasury was briefing about its plans to relocate before the board had formally decided to release this information.

It is certainly unusual for details of company decisions to be released to the media by the government before those decisions have been made.

Investigation

However sources at RBS tell me they do not believe that the government was breaching its commitment not to interfere with corporate decision-making and becoming what is known as a shadow director of RBS.

These bankers also tell me they don't believe this was a case of market abuse, or the illegal release of price sensitive information, because the UK and US stock markets were shut at the time of the briefing.

Even so, an RBS shareholder, Peter de Vink, has today written to the City of London Police Commissioner, the chief constable of Police Scotland, the chief executive of the Financial Conduct Authority and the Lord Advocate of Scotland asking all of them to investigate the release of information relating to RBS's relocation.

RBS had already in previous weeks made the policy decision to move in the circumstances of Scotland seceding.

But it was only in the course of Wednesday, after it learned of Lloyds's decision to brief the Sun, that it decided to formally announce the intention to relocate (and see more here).

The Treasury had known for weeks of this plan to migrate south, because RBS believed it needed primary legislation in parliament to effect it, and the bank had been asking the Treasury whether it would agree to such legislation.

I am told the Treasury had refused to commit to legislate, because the government had made a decision on principle not to make any contingency plans for the possibility of Scotland voting yes to independence.