'Don't forget the anti-freeze!'

Two British explorers are making final preparations before their attempt to become the first to cross the frozen Bering Strait - from Alaska to Russia - in a land vehicle.

Steve Brooks, from Chelsea, west London, and Graham Stratford, from Hereford, will traverse the 56-mile ice bridge in a specially converted vehicle which can float and claw its way back onto the ice if necessary.

Steve has tested his survival suit in the River Thames

The sea is only frozen for about three months of the year and the crossing will be so dangerous the men will have to stay awake throughout the six day journey in temperatures which could dip to -60°C.

They are making the gruelling trip in preparation for an even more arduous challenge - driving from New York to London by heading west across Alaska and through Russia to Europe.

Charitable cause

They leave Britain on Sunday to move into place for the start of the Ice Challenger expedition, which will raise £500,000 for Just a Drop - a charity that provides access to fresh water for families in developing countries.

Mr Brooks, the team leader, told the BBC he needed to prove the Bering crossing was possible for the longer trip in 2002 to be successful.

"The exciting thing is it unlocks the key for us to be the first people to drive right across the planet because if you can't cross the Bering Sea you can't go from the New World to the Old World," he said.

The ice flows north at 3mph and if progress is too slow the expedition could miss the land peninsula and be swept out into the Arctic Ocean.

Arctic temperatures can plunge to -60°C

For the past three years Mr Brooks, a builder, has been working with Mr Stratford, who works with the mountain rescue team in the Brecons in Powys, Wales, to fine tune the detail of the arduous journey.

The men and their Inuit guide will make their way across the unstable mosaic of pack ice in their customised snowmobile, Snowbird 5, which has specially buoyant tanks attached.

Polar bears are another potential hazard but the team are keeping a rifle handy in the cab to deal with any which come too close.

"It is not something we could prepare for ... we are taking a gun with us," said Mr Brooks.

Counting on the weather

Both men will be wearing rubberised survival suits to help protect them from the cold, which will be so severe that exposed flesh can freeze within seconds.

They will also be carrying emergency equipment with them and be in regular contact with the Ice Challenger base in London.

A helicopter will also be on stand by. The expedition could begin any time next week but is dependent on the weather conditions.

An Ice Challenger spokeswoman said: "The colder the weather the better because this will help to stabilise the ice."