A British inventor and entrepreneur has won a $1m (£740,000) prize to help him continue to develop a revolutionary ultra-light, stable carbon fibre wheelchair.

The Mobility Unlimited Challenge has launched three years ago alongside a $4m (£3m) pledge to a range of teams around the world to help change the lives of people with lower-limb paralysis.

As a wheelchair user himself, the Scottish winner of the challenge, Andrew Slorance, 51, was acutely aware of how tipping over backwards was the primary cause of accidents for wheelchair users - and the Phoenix i wheelchair aims to end this.

Tipping over happens "because the wheelchair has a fixed centre-of-gravity, but the user doesn't," Mr Slorance explained.

"If the user moves too far out of sync with the fixed position of the wheelchair, they're going to fall over."

One way to deal with this is by having the axle to the back of the wheelchair and putting the user's weight to the front of it - but this brings new challenges.

When the weight is carried by the small front wheels, this adds drag, making pushing and turning much more difficult, and introducing uncomfortable vibrations that can cause pain and muscle spasms.