We all have a right to a free life and we have to fight for that right - and because we're such freedom lovers, I wrote this song

Sir Paul McCartney

He played his song at an all-star benefit gig in New York a fortnight ago, and has since been overwhelmed by requests to release it as a single.

He has already released From a Lover to a Friend, and will continue to give the proceeds to the Robin Hood Foundation, which distributes funds to families of the victims and to New York's emergency workers.

"We hadn't reckoned on this demand for Freedom but as that's what people want we're getting it out fast to try to raise money for the firefighters and police of New York," said Sir Paul.

'Freedom Lovers'

Sir Paul witnessed the attacks while sitting on an aeroplane at New York airport with his fiancée Heather Mills.

"We all have a right to a free life and we have to fight for that right - and because we're such freedom lovers, I wrote this song at Heather's suggestion," he said.

EMI record plants around the world are now working around the clock to meet the demand for the second single.

Sir Paul: Announced engagement to Mills in July

Sir Paul released From A Lover To A Friend in aid of charity on Monday in the UK.

Written some months ago, it was originally intended to be the first single from Sir Paul's new album Driving Rain.

But Sir Paul decided to release it early to raise money.

More than 300 firefighters are thought to have perished in the collapse of the two towers.

Freedom will be released in the UK next week and in the US soon afterwards.