The Prince of Wales's residence in Gloucestershire, Highgrove House, and Winchester Cathedral were among those plunged into darkness as part of Earth Hour.

Organiser WWF-UK enlisted the support of 28 local authorities to switch off their lights between 8pm and 9pm on Saturday night.

These included London, Birmingham, Plymouth, Coventry, Bournemouth, Cardiff and Norwich.

The lights were also turned off at the Welsh Assembly, Warwick Castle, Brighton Pier, the theatre district of Milton Keynes and all the arcades in Great Yarmouth.

A spokeswoman for WWF-UK explained the event would be repeated again next year when the UN conference on climate change in Copenhagen will be held.

She said: "This year was a warm-up year. We decided we would push it out further in 2009. We are going to send out a big message that people around the world really care."

The event was part of a global campaign, with lights going off at iconic landmarks including the Sydney Opera House and Harbour Bridge.

Earth Hour was started by WWF-Australia in Sydney last year. It saw 2.2 million people and more than 2,100 businesses turn their lights off.