Britain will release on Tuesday a new counter- terrorism strategy called Contest Two, billed as the most comprehensive approach to tackling the threat of terrorism by any government in the world.

Writing in The Observer, Brown said: "We know that there is an al-Qaeda core in northern Pakistan trying to organise attacks in Britain. We know also that there are a number of networks here.

"Al-Qaeda terrorists remain intent on inflicting mass casualties without warning, including through suicide bombings. They are motivated by a violent extremist ideology based on a false reading of religion and exploit modern travel and communications to spread through loose and dangerous global networks".

The new counter-terrorism strategy takes into account recent attacks on hotels in Mumbai. It will reflect intelligence agencies' opinions that the biggest threat to the UK comes from groups aligned or inspired by al-Qaeda.