Britain faces a "wave" of terrorist plots, prepared strategically and directed from abroad by al-Qaeda, Home Secretary John Reid has told the BBC.
Mr Reid said a terrorist attack was "highly likely"
He agreed with MI5 head Dame Eliza Manningham-Buller's assessment that there were 30 major plots, and said an attack in the UK was "highly likely".
New counter-terrorism laws are expected to be among a raft of Home Office Bills at the heart of the Queen's Speech.
Counter-terrorism officials have said Britain is al-Qaeda's top target.
Speaking to BBC Radio 4's Today programme, Mr Reid said Dame Eliza had provided a "salutary warning".
"It is a very great threat. It means that a terrorist attack in the United Kingdom is highly likely," he said.
The government had no information to suggest an imminent attack, he said, but were aware of 30 plots which were "ongoing" and had potential, he said.
"Whereas we thought this was probably haphazard some time ago, they do look as though they are being directed from abroad, specifically by elements of al-Qaeda," he said.
"They look as though they are being prepared strategically and that is that they fit into a pattern... it looks as though there's a wave of such things".
The security service MI5 has increased in size by nearly 50% since 9/11, but Dame Eliza said she was worried it was still not big enough to investigate all suspicious activities.
Last week Muslim convert Dhiren Barot, from London, was jailed for life over an al-Qaeda plot to kill thousands of people in the UK and US.
The UK's top police officer, Sir Ian Blair, said terrorism court cases needed to be sped up, and the 28-day limit for holding suspects without charge needed to be reviewed soon.
Last year Tony Blair suffered the first defeat of his premiership, when Tory, Lib Dem and rebel Labour MPs voted against his attempts to introduce a 90-day limit on pre-charge detention.
There has been speculation the government will try to extend the 28-day limit in the next Parliamentary session.
Mr Reid told the BBC he would be prepared to go back to Parliament to argue the case - but only if the evidence warranted it.
"I have made plain that if it is put to me on the basis of factual or evidential material that there is a requirement to go beyond twenty eight days, that I would be prepared to take that back to Parliament," he said.