By Alan Quartly BBC Moscow

In a sleepy suburb on the outskirts of Moscow a plot is being hatched to send two Britons higher than any human has flown before without actually blasting off in to space.

Above 80,000 feet the pressure is so low that your blood boils... we would die horribly in seconds

Andy Elson, balloonist

Experts from the Zvezda spacesuit factory, regarded as world leaders in their field, are helping balloonists Andy Elson and Colin Prescot get ready for a flight that could take them to a height of 40,000 metres (132,000 feet).

And that would be a new world altitude record.

But to survive in the near vacuum up that high, they have to wear spacesuits, as they plan to travel in an open platform suspended from their huge balloon, QinetiQ 1.

After a week of training at the once top secret factory, Andy Elson explained why the Russian equipment is so vital.

Experts sought

"If we didn't have the spacesuits, we couldn't possibly make the flight.

"Above 80,000 feet (24,000 metres), the pressure is so low that your blood boils and that would be it. We'd die a horrible death in a few seconds."

Boris Mikhailov: "It's a pioneering project... we're really pleased to be involved"

Andy and his team-mate, Colin Prescot, approached the factory about two years ago to ask them for help.

Zvezda, once closed to the outside world, is still under tight security and it is virtually impossible for foreigners to gain access.

It was here, around 40 kilometres (25 miles) from Moscow city centre, that the brightest and best of Russian science battled to beat the Americans into space 40 years ago.

Cosmonaut Yuri Gagarin was fitted out for his spacesuit at the factory before becoming the first man in space in 1961.

The man responsible for that operation, Boris Mikhailov, is still on the staff and is helping the British balloonists get ready for their mission.

Balloon pioneers

Walking through Zvezda's unique museum of space history, with artefacts including Gagarin's spacesuit, Boris says the balloonists are breaking new ground.

"We regarded Gagarin's mission as just everyday work for us engineers.

Russian space suits allow the balloonists to attempt a new record

"When the mission was over, we realised our cosmonauts were pioneers and this was a new completely new area of human activity.

"This is very similar to Gagarin's flight; you can make that comparison. It's a pioneering project and so we're really pleased to be involved."

But a sense of adventure alone won't be enough to make the project successful.

The Zvezda scientists have been putting Colin and Andy through a gruelling programme of testing.

'To die for'

They have to be absolutely sure the spacesuits will not fail. Both balloonists have gone through nine-hour stints in sealed pressure chambers, where the conditions they will face in the stratosphere are simulated.

They breathe in pure oxygen and the suits keep their bodies warm while temperatures outside plunge to nearly minus 50 Celsius.

Rigorous practice prepares the two balloonists for an emergency sea ditch

In another experiment, the men are dropped from a parachute-like harness into a water pool.

They have to know how to survive in the sea should they make an emergency landing.

The flight is due to take place sometime this summer, depending on wind and weather conditions.

The balloon will be launched from on board a ship anchored off the Cornish coast in southwest England.

"For me it's a grand day out, an adventure," says Colin Prescot.

"It's the concept of being up there; two little spacemen on an open deck with the biggest balloon in history, with an ink-black sky and the curvature of the Earth beneath. I would have thought that was something anybody would die for."