A former adviser to David Cameron has been charged with making and possessing indecent images of children.
Patrick Rock, 63, was arrested at his home in London in February after Downing Street contacted police.
Today the National Crime Agency charged the ex-Whitehall adviser with three offences of making indecent images of children and one offence of possession of 59 indecent images of children.
The four charges cover offences said to have been committed between 31 July and 31 August 2013.
Asked about the decision at a post-EU summit press conference in Brussels, the Prime Minister said: "I won't be saying anything.
"It would be purely a matter for the courts and it wouldn't be appropriate to comment."
Rock has been bailed to appear at Westminster Magistrates' Court on July 3.
Judith Reed, a senior lawyer with the Crown Prosecution Service's (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."
The charges facing Rock are:
:: Three counts of making an indecent photograph of a child contrary to section 1(a) of the Protection of Children Act 1978, between July 31 2013 and August 31 2013
:: One count of possession of indecent photographs of children contrary to Section 160 Criminal Justice Act 1988, between July 31 2013 and August 31 2013.
The images have been assessed by Child Exploitation and Online Protection (CEOP) officers and Crown Prosecution Service (CPS) lawyers as meeting the definition of Level C, the NCA said.
Level C is defined as "indecent images depicting erotic posing with no sexual activity", an NCA spokeswoman said.
Rock, a special adviser on policy, was arrested at his home on February 13. He had resigned from his post a day earlier.
Rock has been an influential figure behind the scenes in the Conservative Party for decades, and made three unsuccessful bids to become an MP.
In the 1970s, he was credited with coining the Tory slogan "Cows moo, dogs bark, Labour puts up taxes".
In 2011 Rock was drafted in by Mr Cameron - a fellow adviser to former home secretary Michael Howard in the 1990s - to beef up the Downing Street policy unit.
Prior to his arrest and resignation, Mr Rock had been involved in drawing up Government policy on internet porn filters.