MPs and members of the House of Lords do not have special privileges in law protecting them from surveillance by Britain’s spies, judges have ruled, despite the Home Secretary insisting just days ago that they do.

The widely held parliamentary convention that there should be no tapping of the phones or computers of MPs and peers – known as the Wilson Doctrine – has no legal basis, the Investigatory Powers Tribunal (IPT) ruled.

Theresa May had told MPs on 12 October: “The Wilson Doctrine applies, but of course it is subject to proceedings that are taking place at the moment.”

The ruling from those proceedings sparked anger amongst MPs, prompting emergency questions in Parliament and calls from MPs for statements by John Bercow, the Commons Speaker and the Government.

Harold Wilson tried to clarify the security of MPs’ phones and communications in 1966 (Getty) (Getty Images)

Shadow Commons leader Chris Bryant said: “The freedom of members to be able to speak without fear or favour, and without fear of being spied upon by the Government or any other agency, is a vital part of our being able to do our job as representatives. I think it strikes at the heart of our liberties.”

Scottish National MP Alex Salmond said a cross-party group of MPs are planning a motion to reassert an “essential democratic protection”.

The IPT – senior judges charged with scrutinising the work of the UK’s three secret intelligence organisations – rejected a complaint which accused intelligence officials of illegally trapping their communications. The ruling clarified a doctrine set out by Labour Prime Minister Harold Wilson in 1966, widely interpreted as saying the phones of MPs or peers could not be intercepted save in a major national emergency. Any change to the doctrine would be reported by the PM to Parliament.

However, following claims by the American whistleblower, Edward Snowden, of widespread interception of internet and phone traffic by GCHQ, three politicians mounted a legal challenge.

Lawyers for Green MP Caroline Lucas, Baroness Jenny Jones of Moulescoomb and former MP George Galloway alleged their communications are being intercepted unlawfully under the terms of the Wilson Doctrine.

But the judges ruled against, saying the Doctrine was not enforceable in law. Mr Justice Burton, IPT President, said MPs’ communications with constituents and others were protected, like those of every person, by rules laid down in the Regulation of Investigatory Powers Act 2000. Ms Lucas described it as a “body blow for parliamentary democracy,” adding: “My constituents have a right to know their communications with me aren’t subject to blanket surveillance – yet this ruling suggests they have no such protection.”

Baroness Jones of Moulsecoomb said: “Our job is to hold the executive to account, and to do that effectively it’s crucial people feel they can contact us without their communications being monitored.

Their lawyer, Rosa Curling from lawyers Leigh Day said: “Members of the Houses of Parliament have, for the past half century, relied upon promises made by prime ministers that their communications would be properly protected. [Today’s] judgment shows they were wrong to place any reliance on these.”