Super-toned marathon runner Nell McAndrew and Girls Aloud singer Sarah Harding join forces to promote the Wii

Wii Fit is the latest game for the Wii, the hugely popular Nintendo video console - and it is in massive demand even before it officially goes on sale.

Players use a pressure- sensitive balance board to improve their fitness, strength and balance. The game measures body mass index and fitness before a "personal trainer" guides users through activities including hula hoops, slalom skiing and replicating yoga positions.

When it went on sale in Japan before Christmas, it sold a million copies in five weeks.