The single features stars including Bono and The Darkness

"This is the first time that we have ever paid out ahead of Sunday's charts," said spokesman Warren Lush.

"There is no way Band Aid 20 won't remain top of the tree so we have declared it Christmas Number One five days early."

The charity single has sold more than 600,000 copies since its release.

"Band Aid 20 topping the charts was a five figure loser for us," said Mr Lush.

"We hope all those who backed it to be Christmas Number One... use their money to buy more copies."

Do They Know It's Christmas?, which is raising money to fight hunger in Africa, was outselling its nearest rivals, Kylie Minogue and Ronan Keating, by five to one, according to HMV on Tuesday.

The track, which has been at number one for two weeks already, has now overtaken Eamon's I Don't Want You Back as the UK's biggest-selling single of the year.

The Christmas number one will be announced on Sunday.

Band Aid 20 star Fran Healy is currently visiting south Sudan, where much of the money raised by the charity single will be spent.

The 31-year-old Travis frontman described the conditions as "unbelievable". "They just don't have any water," he said.