Britain's MI5 has revealed that it knows of 30 terror plots currently threatening the UK, and the agency is currently keeping up to 1,600 individuals under surveillance.

|PIC1|Dame Eliza Manningham-Buller, MI5 head, has warned the threat was "serious" and "growing". Potential future attacks could be chemical or nuclear and many of the plots were linked to al-Qaeda, she warned.

British Prime Minister Tony Blair said the terrorist threat was "very real" and explained that there was "poisonous propaganda" warping the minds of young people.

The government has allowed MI5 to increase in size by nearly 50 per cent since 9/11 and now stands at roughly 2,800 staff.

However, Dame Eliza told that the current terror threat will "last a generation" and her concern is that even with MI5's rapid growth, the security service will not be able to investigate nearly enough of the activities it deems to be suspicious.

The latest revelations from MI5 come just days after a UK man was sentenced to at least 40 years in jail for planning a series of attacks. Dhiren Barot, 34, from London, was found to have planned devastating attacks including a so-called "dirty bomb" using radioactive material.

Mr Blair said, "I've been saying, as you know, for several years that this terrorist threat is very real, it's been building up over a long period of time.

"It's not just in this country, as we've seen recently from incidents in India, France, other parts of the world. This is a threat that has grown up over a generation."

Massoud Shadjareh, of the Islamic Human Rights Commission, said he accepted there was a terrorist threat but still urged that the threat had to be put into perspective.

He said, "Over 1,000 arrests have been made under anti-terrorism since 9/11 and out of those, 27 have been found guilty. Out of those 27, only nine have been Muslims," he said.

Dame Eliza said that, since the 7 July bombings, five further major conspiracies in the UK had been thwarted.

"Today, my officers and the police are working to contend with some 200 groupings or networks, totalling over 1,600 identified individuals - and there will be many we don't know - who are actively engaged in plotting, or facilitating, terrorist acts here and overseas," she said.

"Today we see the use of home-made improvised explosive devices. Tomorrow's threat may - I suggest will - include the use of chemicals, bacteriological agents, radioactive materials and even nuclear technology."

"We are aware of numerous plots to kill people and to damage our economy. What do I mean by numerous? Five? 10?

"No, nearer 30 that we currently know of. These plots often have linked back to al-Qaeda in Pakistan and through those links al-Qaeda gives guidance and training to its largely British foot soldiers here on an extensive and growing scale."