Madonna has written a song for the Live Earth gigs

Madonna, James Blunt and Genesis have been lined up to play at the London leg of the global concert series to highlight climate change in July.

But the National Grid said the switch-off stunt could disrupt power supplies across the country.

A National Grid spokesman said they were "keen" for another symbolic idea.

"The organisers had this idea and behaved responsibly by discussing it with us," he said.

Al Gore hopes the global concerts will highlight climate change

"We are used to dealing with surges in demand, as it happens every day around certain TV programmes.

"But it's very difficult to forecast exactly what would happen in terms of demand. We would have had no idea how small or large it would be."

More than 150 of the world's top musicians will take part in the concerts in the UK, America, Australia, Brazil, Japan, China, South Africa, Turkey and Germany.

Organisers in New York are releasing more tickets for their show at the Giants Stadium at 1000 Eastern time (1400 GMT).

More than 200,000 people registered for tickets to the concert at Wembley Stadium.

Tickets for London cost �55 and the profits will go to organisations including the Alliance for Climate Protection, the Climate Group and Stop Climate Chaos.