PEACE activists have called for the closure of a spy base on the edge of the Yorkshire Dales after leaked top secret files appeared to show its staff were involved in a US drone strike in a non-war zone.

The documents, leaked by US National Security Agency (NSA) whistleblower Edward Snowden, suggest British staff at RAF Menwith Hill, near Harrogate, worked closely the NSA in a project codenamed Widowmaker.

A memo to Government Communications Headquarters (GCHQ) staff reveals how US officials ordered a drone strike in Yemen in 2012, to kill a doctor they believed was working with the terror network to surgically implant explosives in suicide bombers.

GCHQ documents handed to The Guardian newspaper reveal workers at the spy base near Harrogate, helped to “discover communications intelligence gaps in support of the global war on terror".

The papers suggest British GCHQ personnel, who work at all levels within both the operational and administrative areas of the North Yorkshire base, were involved in the locating of surveillance targets in Yemen.

A government spokesman said it had a policy of not commenting on intelligence operations.

He said: "We expect all states concerned to act in accordance with international law and take all feasible precautions to avoid civilian casualties when conducting any form of military or counter-terrorist operations.”

Yorkshire MP David Davis said the government needed to clarify the limitations it puts on the use of its intelligence.

He added: "What we are talking about here is murder.

"It may be that you are murdering terrorists and the people are villains, but it is still murder. We don’t countenance murdering criminals in Britain."

CND chairman Professor Dave Webb said it had come as no surprise that staff the base, which is known for its “golf balls” - white radomes which contain satellite antennae capable of intercepting two million conversations an hour - had been linked to drone strikes, the legality of which has been questioned.

He said the allegations bolstered the case for closing the North Yorkshire spy base.

Prof Webb added: "At the least, there should be more openness from the Government about what goes on there, it shouldn't be shrouded in secrecy to the extent it is."