David Cameron’s aide on child internet policy has been arrested for child pornography

One of David Cameron’s closest aides has resigned after being arrested on child pornography allegations.

Patrick Rock has been closely involved in drawing up Government policy on internet porn filters.

He quit after the Prime Minister learned he was at the centre of a police probe over images of child abuse.

Detectives from the National Crime Agency searched No 10 and examined IT systems and offices used by Mr Rock, deputy director of the Downing Street policy unit.

Mr Rock was a protege of Margaret Thatcher and has held a series of senior posts in the Conservative Party. He has been close to Mr Cameron for many years.

Described as the Prime Minister’s ‘policy fixer,’ the unmarried 62-year-old had been tipped as a leading contender for a Conservative peerage only weeks ago.

His arrest and resignation from Downing Street, where he has worked since 2011, will send shockwaves through the party’s high command. The Prime Minister is said to be ‘extremely shocked’.

A friend said: ‘He has known Patrick for a long time and never expected anything like this.’

Mr Rock was arrested last month after officials at No 10 were made aware of a ‘potential offence relating to child abuse imagery’, Mr Cameron’s spokesman told the Daily Mail.

One well-placed source said Mr Rock had also been the subject of a sexual harassment complaint from a civil servant working in Downing Street, which is understood to have been passed to Mr Cameron’s chief of staff Ed Llewellyn.

‘There were accusations against him that didn’t turn into a formal process. That has upset some people at No 10,’ the source said.

Mr Cameron’s relationship with Mr Rock goes back to the Home Office, where they both worked under Michael Howard in the 1990s.

Mr Rock, who has repeatedly tried to become an MP, is known in Westminster for coining the phrase ‘Cows moo, dogs bark, Labour puts up taxes’ used by the Tories in the 1970s.

The Prime Minister brought him back into Downing Street in 2011, a move welcomed by critics as heralding the return of a ‘grown up’ to the centre of government.

In the No 10 policy unit, he has taken a particular responsibility for home affairs issues and has also been involved in drawing up the Government’s measures against internet pornography and child abuse imagery.

In a crusade spearheaded by the Prime Minister, Downing Street brokered a deal with internet firms which means that all 20million households connected to the internet are being contacted and asked whether they want family-friendly filters installed.

Downing Street also persuaded Google and other search engines to introduce changes that will prevent depraved images from being listed in results for more than 100,000 searches.

Downing Street confirmed that Mr Rock, who lives in West London, had been involved in the policy.

‘Patrick Rock was one of a number of advisers and officials involved in dealing with this issue – but the work was led by somebody else, and decisions were taken by ministers,’ a spokesman said.

‘On the evening of February 12, Downing Street was first made aware of a potential offence relating to child abuse imagery. It was immediately referred to the National Crime Agency.

‘The Prime Minister was immediately informed and kept updated throughout. Patrick Rock was arrested at his home in the early hours of February 13, a few hours after Downing Street had reported the matter.

‘Subsequently, we arranged for officers to come into No 10 and have access to all IT systems and offices they considered relevant.

‘This is an ongoing investigation so it would not be appropriate to comment further, but the Prime Minister believes that child abuse imagery is abhorrent and that anyone involved with it should be properly dealt with under the law.’

The spokesman denied suggestions that colleagues in No 10 had been told Mr Rock was ‘off sick’, but only the Prime Minister and a handful of his most senior officials appear to have been told the reason for his absence.

Downing Street refused to comment on the allegation of sexual harassment, but insisted: ‘All complaints are dealt with very seriously and are dealt with appropriately.’