NICOLA Sturgeon is demanding an urgent assurance from David Cameron that rules have not been changed to allow Britain’s top surveillance agency, GCHQ, to spy on MSPs.

It has been claimed that last month security chiefs decided the so-called Wilson Doctrine, which prevents Britain’s surveillance agencies from eavesdropping on MPs, should not apply to the devolved parliaments in Edinburgh, Cardiff and Belfast as well as to the European Parliament.

This means security agencies are now allowed to tap MSPs’ phones and hack their emails.

Ian Murray, the Shadow Scottish Secretary, has tabled a series of parliamentary questions also seeking clarification to what Labour branded an “outrageous” development while Alison McInnes for the Scottish Liberal Democrats called on David Mundell, the Scottish Secretary, to launch an immediate investigation.

The Wilson Doctrine was introduced in 1966 under former Labour Prime Minister Harold Wilson’s government to ban the tapping of UK MPs' and peers' phones; it was later extended to cover emails.

Although the policy was never officially extended to cover the Scottish Parliament and Welsh and Northern Ireland assemblies when they were set up, devolved representatives have been treated in the same way; until, that is last month.

The previous guidelines said: "As a matter of policy GCHQ applies the principles of the Wilson Doctrine to Members of the House of Commons, Members of the House of Lords, UK MEPs, and Members of the Scottish, Welsh and Northern Irish assemblies."

Yet, new ones, apparently issued last month, say: "The Doctrine does not apply to...the interception of communications of Members of the European Parliament or devolved assemblies."

The details emerged as a hearing of the Investigatory Powers Tribunal takes place in London about the protection of elected politicians’ communications from the security services.

Involved in the hearing are Caroline Lucas, the Green MP, and ex-Respect MP George Galloway, who claim it is highly likely their communications were intercepted as a consequence of the surveillance programmes exposed by the CIA whistleblower Edward Snowden.

In her letter, the First Minister expressed concerns, noting how the Scottish Government had not been consulted on the apparent change and urged the Prime Minister to confirm that the Wilson Doctrine remained in place in Scotland.

"I am sure you will agree with me that, excepting truly exceptional circumstances involving national security, the confidentiality of communications between parliamentarians and their constituents is of the utmost importance.

"I am sure you will also agree that it is just as important for MSPs as it is for MPs. This principle of confidentiality is what the Wilson Doctrine was introduced to protect,” she added.

Ms Sturgeon called on Mr Cameron to clarify whether there had in fact been a change in policy and if so when the decision was taken and who was aware of it.

She also sought assurances that if the change had been made, that it should be reversed and MSPs treated equally to MPs.

Iain Gray, Scottish Labour's acting leader, was irate, saying: "It is utterly unacceptable for the communications between devolved representatives across the UK and their constituents to be monitored by GCHQ.

"There needs to be full transparency from the UK Government on this. We need to know urgently who decided on this major rule change and when.

"For the rules on spying on elected representatives across the UK to change without any sort of public scrutiny or accountability is a democratic outrage.

"We also need to know from each of the devolved administrations what, if anything, they knew about this change," he added.

Ms McInnes insisted the security services should be focused on catching terrorists, not spying on MSPs.

“We know the Tories have an utter disregard for our basic civil liberties but this seems to show a government spiralling out of control in its clamour for power.”

Calling on Mr Mundell to launch an immediate investigation, she asked whether or not the change had been sanctioned by the PM.

“That such clandestine actions may also be taking place in elected legislatures in Wales, Northern Ireland and the European Parliament will be puzzling and offensive to many people who understand the UK as a parliamentary democracy, not a dictatorship.This once again shows why you need Liberal Democrats to stand up against illiberal attempts by the state to monitor law-abiding citizens.”

Murdo Fraser for the Scottish Conservatives noted: “Given the SNP devised the state guardian scheme and wants to meddle in people’s lives to ludicrous extents, you’d think the party would welcome these reports.

“Perhaps the Nationalists should think of this as being given a little named person of their own,” he added.