It follows fears raised by a similar US radar early warning system which is at the centre of an investigation into a cancer cluster.

The role of the North York Moors station is due to be expanded as part of the United States' "Son of Star Wars" missile defence system.

With fears increasing about what changes to the RAF Fylingdales base will mean to local people, BBC News Online looks at the American proposals.

What is the role of Fylingdales?

The RAF Fylingdales site in North Yorkshire was first opened in the 1960s as a Ballistic Early Missile Warning System.

It became famous for its three golf-ball shaped radars which have now been replaced by a pyramid structure (containing?) an advanced radar capable of tracking missiles launched by rogue states or terrorists.

Data produced at the site is shared between the British and American governments.

What do the Americans want to do at Fylingdales?

President Bush has asked to use Fylingdales as part of an early warning missile defence known as "Son of Star Wars" after Ronald Reagan's original "Star Wars" strategic defence initiative.

It would enable rockets from Russia, China or the Middle East to be spotted early in their trajectories, so they could be intercepted.

Although Fylingdales can already track satellite launches, it would need to be upgraded for the new role.

What have British politicians said about the plans?

Defence Secretary Geoff Hoon has said the missile system at Fylingdales could represent "an invaluable extra insurance against the development of a still uncertain but potentially catastrophic threat to the citizens of this country".

He believes involvement in the project would not prejudice British interests.

But opponents say the scheme is unnecessary, would not work and would simply make the UK a target - without giving it a protective screen of missiles.

What are the health fears?

A US Air Force researcher has said radiation from the current radar system may have carcinogenic properties, and a study is taking place into an apparent cancer cluster at a similar base in Massachusetts.

But Armed Forces Minister Adam Ingram told residents at a recent meeting that there was no need for the Government to wait for the American survey results because current scientific evidence does not support the claims.

Residents also say the radiation levels have not been monitored since a new radar system came into operation nine years ago.

Would there be an increased risk of a terrorist attack at Fylingdales?

The US plan to use Fylingdales as part of its missile defence programme will not change the threat of an attack on the base, the Defence Secretary has said.

Mr Hoon believes the enhanced security arrangements put in place over the last 18 months should be sufficient to defend the base.

He has also said there has been no request by the Americans to launch anti-ballistic missiles from Fylingdales.

Will the upgrade go ahead?

A Ministry of Defence commissioned report has said the Fylingdales upgrade does not need planning permission because it would not alter the appearance of the radar, increase radar emissions, or affect the local environment.

The North York Moors National Park Authority agreed and gave the go-ahead for the work.

Boeing won the contract to carry out the work, which includes installing faster computers, new communication links and modern graphic displays.