Half the money raised will go to the McCanns' fund to find their daughter, with the other half split between the charities Missing People and Missing Children Europe.

Supporters of the couple from Rothley, Leicestershire, will also launch 1,000 glowing paper lanterns into the night sky in Britain, Portugal and the US to coincide with the anniversary of Madeleine's disappearance.

Sir Richard has offered his support

Almost £2m was raised for Madeleine's Fund in the first 10 months after she went missing from Praia da Luz in Portugal in May 2007.

But as the number of donations lessened her parents spent hundreds of thousands of pounds hiring a series of private detectives to continue the search.

McCann family spokesman Clarence Mitchell stressed there was no "crisis" in the fund, which currently stands at approximately £500,000.

Mr Mitchell said the west London dinner would be attended primarily by the couple's friends and long-term supporters, including their millionaire backer Brian Kennedy.

The paper lanterns will be launched at 7.30pm British time from about 20 different locations, including Praia da Luz, Rothley and Mrs McCann's hometown of Liverpool.