The 18-year-old was due to perform at Thursday's NME magazine awards in London, and to present a prize at next week's Brit Awards.

She has a whole crew and band to think of and she has decided not to take the risk Kelly Osbourne's spokeswoman

But the daughter of former Black Sabbath frontman Ozzy opted not to fly to London after her British-born parents said they feared for her safety,

Her spokeswoman said: "Kelly's parents were in New York on 11 September when the Twin Towers came down so you can imagine how they feel.

"The decision wasn't taken lightly and Kelly has thought long and hard about it."

Osbourne, who is currently at number 18 in this week's singles chart with her second single Shut Up, was "upset" about the decision, her spokeswoman added.

"But as well as herself and her parents, she has a whole crew and band to think of and she has decided not to take the risk," she said.

Osbourne shot to fame on the TV docusoap The Osbournes, which followed the lives of her parents, herself and younger brother Jack. Older sister Aimee declined to take part in the programme.

About 450 troops and 1,700 extra police officers began guarding Heathrow Airport on Tuesday, and the use of troops in the centre of London has not been ruled out.

The government said it was acting on intelligence information, but Home Secretary David Blunkett said the public should be "alert, not alarmed".