Elton and David rush to the altar

David Furnish and Elton John, with sons Zachary and Elijah. Photo / Getty Images

Celebrities line up to see superstar and partner tie the knot.

Superstar Sir Elton John and David Furnish are to marry Christmas week in a "small and intimate" ceremony, nine years after exchanging vows for their civil partnership.

John, 67, and Furnish, 52, have invited 50 friends and family to their Windsor home to witness them tie the knot on December 21, says the Daily Mirror.

It's reported that David and Victoria Beckham, Elizabeth Hurley and Ozzy and Sharon Osbourne will be among about 50 guests.

The couple's sons, Zachary, 3, and 1-year-old Elijah, will be ring bearers, according to a friend.

"Elton and David have been planning this for months.

"Elton is flamboyant but, for once, this will be a decidedly low-key affair," the friend said.

"Only close friends and family are invited - it's going to be a small, intimate do."

On Wednesday it became legal to convert civil partnerships into marriages in Britain.

In 2005 the pair, now together for more than 20 years, became one of the first British couples to have a civil partnership, the Mirror said.

That service was at Windsor Guildhall, before 650 guests, followed by a champagne-fuelled knees-up at home.

In September last year, John told Ellen de Generes on her eponymous talk show about why the couple will get married even though they've had a civil partnership ceremony.

"We had our civil partnership on the first day it was legally possible. You know, same-sex people have been waiting a long time for things to happen for them. And have been through hell. So when a government gives you this legislation, which is so wonderful, then you seize it by the horns.

"We won't have a big wedding, because we've already done that with our civil partnership."