A top British government aide who helped create 10 Downing Street’s controversial policy to censor online pornography for the majority of British Internet users has resigned from his post on Monday after being arrested last month on charges of possessing child pornography.

Patrick Rock, a longstanding Tory adviser to Prime Minister David Cameron, had served as the deputy director of policy.

The prime minister’s office confirmed to British press that it had been “made aware of a potential offense relating to child abuse imagery” on February 12, and Rock was arrested the next day at home.

“Subsequently, we arranged for officers to come into No 10 and have access to all IT systems and offices they considered relevant,” an anonymous spokesperson was quoted in UK media as saying. “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.”

However, the same spokesperson played down Rock’s role in drafting the policy on online filters, which as of January was shown to be overblocking.

“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,” the spokesperson said.