Police have expanded their use of powers to force suspects to decrypt files by 50 per cent in the last year, figures released today reveal.

In the 12 months to March 31 this year, government officials approved 38 notices under Part III of the Regulation of Investigatory Powers Act, compared to 26 in the previous year.

The powers, known as section 49 notices, require suspects to hand over passwords or make files intelligible to investigators on threat of a two-year jail sentence, or five years where national security is concerned.

As well as obtaining more section 49 notices, police also expanded the range of crimes they were used to investigate.

In 2008/09 they were served in relation to counter-terrorism, possession of indecent images of children and "domestic extremism" (a case involving activist attacks on animal testing labs). In the last 12 months, however, RIPA Part III was used to demand decryption in cases of insider dealing, illegal broadcasting, theft, excise duty evasion and aggravated burglary, the Chief Surveillance Commissioner Sir Christopher Rose said in his annual report.

Investigations into indecent images of children remained the "main reason" section 49 notices were served, he added.

Of the 17 notices obtained this year that have so far been served, six suspects complied and seven did not. The remainder are still being processed. One person suspected of possessing indecent images of children has been convicted for failing to hand over passwords.

The compliance rate was up on last year, the first full year since the powers were activated, when 11 out of 15 suspects served with a section 49 notice did not make their files intelligible to investigators.

Sir Christopher noted the discrepancy between 38 approvals granted by the National Technical Assistance Centre (NTAC) and the number of notices actually served. NTAC is a unit at GCHQ, the Cheltenham code-breaking agency.

"Notices, once approved, should be served without delay," Sir Christopher said. "If delays continue, I will require an explanation."

Last year The Register reported the case of the first man known to have been jailed for failing to hand over encryption keys to the police. "JFL" was a schizophrenic software developer initially charged with explosives offences that were later dropped. He was sectioned under the Mental Health Act during his prison sentence. ®