The home secretary is preparing to unveil new anti-terror measures, thought to include the use of secretly-taped phone calls as evidence.
MI5 is advertising for new recruits on its website
Other changes are predicted to include the hearing of parts of some trials in secret, without a jury.
David Blunkett told BBC's Newsnight he had been told it was inevitable the UK would face a terrorist attack.
On Wednesday he will detail the expansion of MI5, with 1,000 new staff, many of them Arabic and Urdu speakers.
Mr Blunkett told the BBC the security services needed more powers to apprehend terrorists before they strike.
But MPs will debate criticisms of current laws allowing foreign terror suspects to be detained without trial.
Some of the anti-terror powers introduced after the 11 September attacks only last until 2006.
Mr Blunkett says the paper will show what other countries are doing and recommendations from reviews of current British laws.
He suggested the law could be changed to allow secretly-taped phone conversations to be used in court.
Hearing some cases partly in secret before specially-vetted judges with no juries so intelligence sources are not compromised, is among the ideas likely to be included.
Pre-emptive action against terror suspects
Civil action against those on the fringes of terror groups
Specially-vetted judges for sensitive evidence
Part-secret trials for Britons
Defendants could also be barred from hearing certain evidence mirroring what happens for foreign terror suspects.
The Home Office insists no decisions have been taken on the proposals, which have sparked criticisms from lawyers and human rights groups.
Mr Blunkett said the head of MI6 had told him a terror attack on Britain was a case of not "if" but when.
"Whatever we do - and we are doing everything we can - we cannot guarantee, and nor should we pretend to, that we can protect ourselves forever by security measures alone," he told BBC Two's Newsnight.
Standard of proof?
Apprehending suspects before they struck could give anti-terror efforts a very good chance, he argued.
This suggests the paper could include allowing Britons and other nationals to be convicted of terror offences based on intelligence reports alone.
But he does not intend to lower the standard of proof for terror cases, although there could be civil court orders for those on the fringes of terror groups.
Details of the positions have been posted on MI5's website
Mr Blunkett insisted he wanted to protect democracy and appealed to his critics to come up with answers.
"We all accept that this is an enormous challenge - the proportionality, the balance between protection of individual rights and the protection of the nation from terrorism attack," he said.
"Now you tell me how to square the circle."
On Wednesday MPs will debate criticisms about the anti-terror laws published in December made by a review group chaired by Lord Newton.
The group said detention without trial had not been used excessively but
pushed for the laws to be replaced by measures which did not need Britain to opt out of European human rights laws.
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On Tuesday Parliament's human rights select committee said it doubted whether the detentions were justified and argued measures in line with Britain's human rights duties were urgently needed.
Amnesty International UK's Lesley Warner said the current laws for foreign terror suspects had faced universal condemnation.
"The home secretary's reported new proposals are an aberration of justice, the rule of law and human rights," she said.
On Thursday, the laws come up for their annual renewal from Parliament.
On Wednesday Mr Blunkett is also due to spell out his plans to recruit another 1,000 staff for MI5 as it shifts to recruit more Arabic speakers and focus on the threat from al-Qaeda.