Because the system only controls the game's controller, and not the game itself, it can be used with any Playstation game. The game pauses while the controller is inactive.

Two players can use different steppers and controllers to play two-player games. The machine also has a parental over-ride and is aimed at youngsters under the age of 12.

'Limit access'

Dr Campbell said: "We know children are not as active as they need to be.

"Anything that encourages them to exercise has to be helpful. However, how sad that we have to bribe children into physical activity. It's a terrible indictment on our society.

"I don't think this is a bad invention but I don't think it's ideal.

"It would be far better to encourage an increase in physical activity across the board, at both school and at home. And it might be an idea for parents to limit their children's access to the computer."

Dr Colin Waine is chairman of the National Obesity Forum and is in favour of the invention, claiming it could help prevent children becoming obese when they reach adolescence.

"Physical inactivity is one of the major causes of the rise in obesity so anything that means children will be more active is to be welcomed.

"Sport doesn't appeal to everybody and we have got to think beyond the playing field.

"This machine is a novel way of getting children to be more active. I don't think it's a bribe, it's just an incentive."

Rick Dalton is director of Gymkids, the company which has launched the machine.

He said: "Unfortunately, the reality is that I don't think we are ever going to totally convince children to put away the Playstation in favour of running around outside.

"Step2Play combines both activities and, whilst it isn't an alternative to outdoor play and exercise, it is one way of combining a previously sedentary activity with a bit of movement and exercise."