Jacqui Smith's estimate came as she argued for an extension of the time authorities are allowed to hold terror suspects without charge.
"We now face a threat level that is severe. It's not getting any less, it's actually growing," Smith wrote in the editorial to be printed in The News of The World tabloid. "There are 2,000 individuals (police and security agencies) are monitoring. There are 200 networks. There are 30 active plots."
The News of The World originally carried a quote from Smith which read that 22,000 individuals were being monitored, but it sent out an e-mail late Saturday saying the correct figure was 2,000.
Smith said the figures represented an increase over the past two years, although they were nearly identical to estimates made by the leadership of Britain's domestic spy agency, MI5, in 2007 and 2008.
In 2006, Eliza Manningham-Buller, the then-head of MI5, said officials knew of about 30 terror plots and were keeping 1,600 suspects under surveillance. The number of suspects was revised upwards to 2,000 in 2007 by Jonathan Evans, the current head of MI5.
Smith faces an uphill battle to persuade lawmakers to pass a law allowing police to hold terror suspects up to 42 days without charge. Such suspects can currently be held up to 28 days, and Smith has often invoked the growing threat of terrorism -- and the increasing complexity of terror plots -- to justify the extension of time.
However, the proposal is fiercely opposed by civil libertarians and even some members of her own ruling Labour Party.
Tony Blair was handed his first parliamentary defeat as prime minister in 2005 when lawmakers rejected his plan to increase the limit to 90 days, settling on a compromise of 28 days. Some analysts have suggested the current prime minister, Gordon Brown, could also founder in his attempt to extend the limit.
But Smith said the extra time was needed like never before.
"Since the beginning of 2007, 57 people have been convicted on terrorist plots. Nearly half of those pleaded guilty so this is not some figment of the imagination," she said in the article, a preview of which was made available Saturday.
"It is a real risk, and a real issue we need to respond to."
