Peace campaigners demanded to know yesterday why a heavily armed foreign military aircraft that crashed in the Norfolk countryside was allowed to carry out manoeuvres over Britain.

The United States Pave Hawk helicopter was flying low when it crashed on Tuesday night, killing its four occupants.

Wreckage including live ammunition was scattered over a wide area at a nature reserve in Cley-next-to-the-sea.

The helicopter had taken off from RAF Lakenheath in Suffolk, Britain's biggest US military base.

Investigators were scouring the site of the crash which was cordoned off and the public were banned from the area.

Campaign for Nuclear Disarmament general secretary Kate Hudson said: "The news of a US military helicopter crash this week is a tragedy for family and friends of the crew.

"It is also a stark reminder of the presence of US military bases in the UK.

"While an area of some 400 square metres is cordoned off due to the presence of ammunition at the crash site, much of the British public will be left wondering why armed US helicopters are flying over the British countryside by night.

"These US military bases operate with no degree of accountability or parliamentary oversight.

"They include a spy base at Menwith Hill in Yorkshire, RAF Croughton which shuttles communication intercepts and has supported US drone strikes in Yemen as well as RAF Lakenheath and RAF Mildenhall which have been used as staging posts for US military operations around the world, including Iraq and Afghanistan.

"The anti-nuclear movement celebrated the removal of the last remaining US freefall nuclear bombs from RAF Lakenheath in 2008, but it is astonishing that these catastrophic weapons remained on UK territory as recently as six years ago.

"From Greenham Common to Lakenheath, public pressure has brought unwanted attention on these secretive bases resulting in the removal of nuclear weapons from both.

"But we must do more to bring these facilities into the light by scrutinising their operations and demanding an end to foreign military forces operating on UK territory."

Campaign for the Accountability of American Bases co-ordinator Lindis Percy said: "It is awful that this happened with the loss of four lives.

"One question to ask however is why was this US helicopter, flown by members of the US visiting forces, allowed to carry a large amount of ammunition and did the British authorities know about this?

"As usual, anything to do with the US military is shrouded with secrecy and we may never know what happened as the US military will want to take over the investigation themselves."