The pair will wear Russian-made full pressurised spacesuits for the trip

Colin Prescot and Andy Elson plan to soar 25 miles (132,000 feet) to the edge of space in the 1,270 foot (387 metres) tall balloon, QinetiQ1.

Last summer's planned launch from a vessel off the north Cornwall coast was called off because the ideal weather window failed to materialise.

But now sponsors QinetiQ have confirmed that they will make another attempt some time between June and September from the same location off St Ives.

'Ultimate challenge'

The balloon will consist of about nine acres of super thin plastic and will be 400 times the size of a typical hot-air balloon and as tall as the Empire State Building; or seven times the height of Nelson's Column in London.

The pair will be making their ascent on an open flight deck and the whole should be completed within nine hours.

They will carry enough oxygen to last for 11 hours.

The duo will remain seated all through the flight and will perform radiation and micrometeoroid experiments and Mr Prescot will try to fly a solar-powered propeller-driven plane in the stratosphere.

A 72-hour weather window is required to prepare for and stage the launch.

Inflation tests have already been carried out on an 88th scale version of the balloon.

Confidence inspiring

The scaled down version took five hours to inflate at QinetiQ's hangar in Somerset, during which the envelope was subjected to stress tests.

Colin Prescot said seeing the true shape and form of the balloon for the first time "really inspired our confidence in the success of the mission".

Mr Prescot, 51, from Stockbridge, Hampshire, a balloonist for the last 25 years, has described the planned 12-hour trip on QinetiQ1's open flight deck as the "ultimate challenge".