The lights behind Big Ben went dark for an hour tonight as the UK took part in Earth Hour.
The Houses of Parliament and the London Eye on the opposite bank of the Thames joined Buckingham Palace and world landmarks including the Eiffel Tower and Sydney Opera House in switching off their lights for 60 minutes to mark the World Wildlife Fund campaign.
Other UK landmarks due to take part to raise environmental awareness included Tower Bridge, Edinburgh Castle, Brighton Pier, Durham Cathedral and Windsor Castle.
In London the event was marked by a flashmob of 60 people dressed as pandas before singer Sophie Ellis-Bextor played a concert in front of the London Eye, with the performance streamed live on YouTube.
Wearing a dress covered in solar-powered lights, she joked to fans: "There is normally a great view of Big Ben from here but for some reason it is in darkness."
Dougie Poynter from pop group McFly was also involved in the event.
Earth Hour was launched in 2007 in Australia and has since spread around the world.
Last year 10 million people in the UK took part, WWF said, as part of a record-breaking chain of more than 7,000 towns and cities in 154 countries.
This year's symbolic switch-off started in Samoa and swept around the planet via major cities of the world all turning off their lights at 8.30pm. The last place to do so will be Tahiti.
Register for free to continue reading
Registration is a free and easy way to support our truly independent journalism
By registering, you will also enjoy limited access to Premium articles, exclusive newsletters, commenting, and virtual events with our leading journalists
Already have an account? sign in
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies