Theresa May and Kenneth Clarke urge Tories to back security plan

Ministers tell party to support government on surveillance and claim access to sensitive data is crucial to deport terror suspects
UK passport
Terror suspects could be given UK passports if the government is not able to fight their deportation using sensitive data, Ken Clarke and Theresa May claim in their letters. Photograph: Gary Roebuck /Alamy

Theresa May and Kenneth Clarke have launched a joint bid to win the backing of Tory MPs for their plans to strengthen the powers of the security services, after they were widely criticised as taking a step towards secret justice.

The home secretary and justice minister, have sent letters to their parliamentary party claiming that terror suspects could be given British passports if the government is not able to fight their deportation using sensitive evidence.

The four-page letter has angered some senior Tories who believe it is a desperate bid to shore up proposals that have been condemned across the political spectrum. It also raised eyebrows because May and Clarke have clashed a number of times over human rights.

May and Clarke wrote that the inability for cases to be heard under "closed material proceedings" – in which defendants are not shown evidence against them and rely on security-vetted lawyers called special advocates – would leave the government unable to deport terror suspects or deny them a passport, because it could not reveal sensitive evidence in open court.

The pair wrote: "In judicial reviews … there is no statutory basis for closed material procedures to be available to the court. This means the government is unable to fight the case and may have to allow British citizenship to an individual believed to be engaged in terrorism-related activity."

The letter also deals with the government's attempts to widen surveillance of communications, claiming that the intelligence agencies can no longer monitor a quarter of all communications data as a result of technological advances.

May and Clarke say criminals are using internet-based communications such as Skype and instant messaging rather than making phone calls, which can be traced under existing powers.

"We estimate that we are now only able to access some 75% of the total communications data generated in this country, compared with 90% in 2006. Given the pace of technological change, the rate of degradation could increase, making future capability very uncertain," they wrote.

Dominic Raab, the Tory MP for Esher and Walton and a campaigner on civil liberties, said that the letter has failed to address the concerns of many MPs.

In a further development, claims have emerged that the US withheld information from MI5 and MI6 about a possible terrorist plot because they feared British courts would reveal evidence of wrongdoing by foreign intelligence agencies.

According to the Daily Telegraph, the CIA warned Britain's security and intelligence agencies that al-Qaida was planning an attack 18 months ago but withheld detailed information. It quoted security sources saying the US move was in retaliation for a decision by UK courts to disclose a brief summary of CIA information.

That information confirmed that Binyam Mohamed, a British resident secretly flown to Guantánamo Bay, had been brutally treated. The CIA information was passed to MI5 and MI6, who fought unsuccessfully to suppress it.

The article on Thursday described MI6 as being particularly "frustrated" after receiving "only the tip not the intelligence" about an alleged plot, which was said to have echoes of the Mumbai attack in 2008 in which 174 people died.

Government officials talk of the US withholding "little pieces" of intelligence information. They suggest the US move led to unnecessary use of British counter-terrorism resources but concede that the US would never withhold life-threatening intelligence.