Their countries were at the forefront of Nato's Libyan operation.

They will meet National Transitional Council (NTC) leaders in Tripoli, before flying to Benghazi, where they are expected to speak in the former rebel stronghold's Liberty Square.

NTC chief Mustafa Abdul Jalil has pledged "the leaders... will be safe".

At the airport, Mr Cameron said he was delighted to be in Tripoli, adding that he "hoped to work for a better and free and democratic Libya".

He and Mr Sarkozy then boarded a French helicopter to visit a hospital in the capital. The two leaders are hugely popular in Libya, where common graffiti slogans include: "Merci Sarkozy!" and "Thank you Britain!"