Brown hits back at al Qaida threats

"Nothing can justify either threats to the United Kingdom or any form of terrorist activity and it must be the right of the United Kingdom to make its own decisions on all these issues," the Prime Minister said.

His comments came after Osama Bin Laden's number two warned al Qaida would strike in retaliation for the award of the honour to the controversial author.

Ayman al-Zawahri, the terrorist network's deputy chief, accused the UK on Tuesday of defying the Muslim world.

Mr Brown spoke out at a Downing Street press conference alongside UN Secretary General Ban Ki-Moon who is on his first official visit to the UK since succeeding Kofi Annan.

One of Iran's most revered Shia clerics condemned the knighthood as "a very, very vast action against Islam" and said it would give terrorists a pretext to attack Britain.

Grand Ayatollah Yusef Saanei told Sky News: "When your Queen awards Salman Rushdie and turns him into a knight, what do you expect? This is a blasphemy. This is an insult to all the prophets of the world.

"Apart from the fact that this issue insults all the religions of the world, this will also give a pretext to the terrorists. The terrorists can use this as a pretext to do something against (Britain). This act of the Queen is a very, very vast action against Islam."

Government minister Tessa Jowell, who was culture secretary at the time Sir Salman's knighthood was announced, told Sky: "Salman Rushdie was recognised in the recent honours as one of this country's outstanding writers.

"In times when terrorist threats beset the way of life in this country and the way of life in this country is being attacked by terrorists, standing up for free speech and freedom of speech is ever more important."