The prime minister's communications chief Andy Coulson has resigned.
Coulson has faced pressure after revelations about phone hacking by News of the World journalists while he was editor of the newspaper.
David Cameron had backed him and said he regretted that Coulson had felt compelled to step aside.
Coulson was a key part of Cameron's inner circle after joining the Conservative leader's team in 2007.
He said it had been "a privilege and an honour to work for David Cameron for three-and-a-half years".
But he added: "Unfortunately, continued coverage of events connected to my old job at the News of the World has made it difficult for me to give the 110% needed in this role.
"I stand by what I've said about those events but when the spokesman needs a spokesman, it's time to move on."