British police and security agencies are keeping tabs on 30 terror plots, Home Secretary Jacqui Smith told a Sunday newspaper.
"There are 22,000 individuals who are being monitored. There are 200 networks involved and 30 active plots," Smith said in an interview with the News of the World.
"We now face a threat level that is severe. It's actually growing," said the interior minister.
Smith said the level of threat showed why the British government is seeking legislation to extend the detention of terror suspects to 42 days from the current 28-day limit.
The measure faces strong opposition in parliament from the opposition Conservatives and Liberal Democrats as well as rebel lawmakers from the ruling Labour party.
"We task the police and the security agencies with protecting us. Frankly, if they say to me it's getting more difficult and we need more time to investigate thoroughly, it is my duty to provide them with the tools they need," Smith said.
"We can't wait for an attack to succeed and then rush in new powers. We have got to stay ahead.
In 2005, four British suicide bombers killed 52 people on underground trains and a bus in London.
The minister also confirmed she would announce a scheme next week to bring over moderate Islamic clerics from Pakistan to assist British imams in combating extremism in their communities.
"The vast majority of British Muslims have a Pakistani heritage. If we work with the government there we can win the arguments," said Smith, who visited Pakistan this month.