A former senior adviser to the prime minister has been charged for possession of child abuse images.
Patrick Rock was arrested at his home in London in February after Downing Street officials first contacted the police.
The 63-year-old has been charged with three counts of making indecent photographs of children and of possession of 59 indecent images of children.
He was questioned by investigators from the newly formed National Crime Agency.
Police searched offices and computers in Downing Street as part of their investigation.
The images have been assessed by Child Exploitation and Online Protection (CEOP) officers and CPS lawyers as meeting the definition of level C - the lowest category.
Level C is defined as "indecent images depicting erotic posing with no sexual activity", an NCA spokeswoman said.
Judith Reed, a senior lawyer with the CPS organised crime division, said: "The decision to prosecute has been taken in accordance with the Code for Crown Prosecutors.
"We have determined that there is sufficient evidence for a realistic prospect of conviction and that a prosecution is in the public interest.
"May I remind all concerned that Mr Rock has a right to a fair trial. It is extremely important that there should be no reporting, commentary or sharing of information online which could in any way prejudice these proceedings."
Mr Rock was deputy head of David Cameron's policy unit at the time of his arrest. They worked together as special advisers and have known each other since the late 1990s.
At the time of his arrest, Cameron, who was a long-standing friend of Rock, was forced to issue a statement: "When I heard about these allegations I was profoundly shocked and I remain profoundly shocked today.
"I have to be careful about what I say about this issue because a criminal investigation is under way."
Responding to questions regarding the charges made against Mr. Rock during a news conference in Brussels, the Prime Minister declined to comment saying: "I won't be saying anything. It would be purely a matter for the courts and it wouldn't be appropriate to comment."
Mr Rock was dubbed "'the most powerful Cameron adviser most people have never heard of", and played a key role in shaping government policy on internet filters to stop children accessing pornography.
He failed to win a seat in Parliament on three separate occasions in the late 1970s and early 1980s.
He has been bailed to appear at Westminster Magistrates' Court on 3 July.