Alex Carlile, a House of Lords member who is responsible for reviewing Britain's legal efforts to combat terrorism, sharply criticized European Court of Human Rights rulings he claims are hampering security.
The court has ruled that some foreign terror suspects can't be sent home if there is a risk they may be mistreated or tortured.
In May, European law prevented the alleged ringleader of an al-Qaida bomb plot and another man regarded by authorities as a serious threat to national security from being sent by Britain to their native Pakistan.
"The effect is to make the U.K. a safe haven for some individuals whose determination is to damage the U.K. and its citizens, hardly a satisfactory situation," Carlile said in an annual report.
Unlike many other European countries, Britain does not permit wiretaps to be used in evidence - meaning it has been unable to prosecute several suspected terrorists.
The European rulings means the U.K. has also been prevented from deporting some of them.
To circumvent the European law, Britain has asked countries to sign agreements pledging not to mistreat suspects deported there, including Algeria, Jordan and Ethiopia. A pact struck with Libya is currently on hold after it was challenged by Britain's courts.
Carlile, who is stepping down from his role, also said he backed the government's decision to replace its house-arrest style program for those who can't be charged or deported with a similar, but less stringent package.
Home Secretary Theresa May announced last week that the unpopular control orders system, under which a person could be held under curfew for up to 16 hours per day, would be overhauled.
A new system will require suspects to wear an electronic tag, stay at a specific address overnight for about eight to 10 hours and restrict an individual's Internet access.
"All the main political parties now accept that a system is required to protect the public against a small and potentially very dangerous cohort of individuals," Carlile said.
Britain's junior coalition party, the Liberal Democrats, had previously pledged to scrap the restrictions outright. Prime Minister David Cameron's Conservatives had also raised serious objections.
Carlile said opposition lawmakers often had too little information about the scale of the terrorism threat to make credible policy decisions.
He said opposition parties should appoint one or two lawmakers who would be vetted by Britain's spy agencies and allowed better access to intelligence. Security officials currently offer opposition lawmakers only limited briefings on the intelligence matters.
Improving their access to spy agencies would take "some of the political steam out of what at times has been a poorly informed debate," Carlile said.