Put that Christmas light out!

But as Oxford Street prepares to switch on its illuminations tonight, it seems not everyone is satisfied by the environmental credentials.

The Liberal Democrats claim that a mini forest of trees would have to be planted to compensate for the carbon emissions generated by the West End's two miles of festive lights.

Despite boasts the illuminations are greener than ever, they say that the combined "carbon footprint" from the Oxford Street and Regent Street lights would take 215 trees 100 years to "offset".

Tonight's festivities on Oxford Street - continuing a tradition begun in 1959 - will see pop band All Saints perform the official switch-on at 6pm outside Selfridges.

And Jordan and Peter Andre will perform their Christmas single.

But Mike Tuffrey, Lib-Dem group leader on the London Assembly, said: "With the Oxford Street lights being switched on earlier every year and left on during the day, they are using a significant amount of energy."

He called for event organisers, the New West End Company, to do more to power the lights by renewable electricity.

He added: "They could also offset the Oxford and Regent Street lights' carbon emissions for just over £2,000 a year, a small price to pay compared to the cost of putting on the show and one worth paying to celebrate Christmas with a clear conscience."

According to the Lib-Dems, the lights in the two streets, which remain on until 6 January, will produce 43 tonnes of carbon dioxide.

But a spokesman for the New West End company said both streets were using lowenergy bulbs with 40 per cent less emissions than before.

The Oxford Street lights will remain on 24 hours a day while those in Regent Street are on between 2pm and 2am.

They are expected to help attract about 40 million shoppers over the next six weeks.

They can sponsor a bulb under the Light Up London campaign, with proceeds going to charity. Donations can be made at: www.heart-1062.co.uk/lightuplondon or from the christmas shop and food hall at Selfridges.