It's amazing - when I do nothing it just floats to and fro

Stephen Bradshaw, Spinal Injuries Association

Most of the time, it can be run on all four wheels like an ordinary wheelchair, but the user can lean it onto the back two when stairs are encountered.

And while it looks as if the user is performing daring "wheelies", he or she is actually completely in control.

One of the biggest disadvantages of being in a wheelchair is that you cannot conduct conversations eye to eye - or reach above normal shoulder height.

Once the two-wheel position has been achieved, the seat can be raised.

High cost

The expected cost of the chair, at �20,000 could be prohibitive for many disabled people.

However those who have tried it are enthusiastic.

Stephen Bradshaw, from the Spinal Injuries Association, said: "It's amazing - when I do nothing it just floats to and fro."

"With a device like this, I can zip down to the shops, zip back, and reach something off a much higher shelf.

"I don't have to ask other people for help, so it will improve my independence very considerably. I love it."

Kerbs are obviously no problem for the machine, but most steps can also be tackled.

David Coates, from Johnson and Johnson, said that the extra maneouvrability would save users money in home adaptations.

He said: "We have used state of the art technology that keeps helicopters and aircraft in the air."