UK National Security Adviser resigning – 2 months in?

That’s what the Mail has this morning, at least:

Sir Peter Ricketts, who was givent the newly created role just after Cameron took office, has made the surprise announcement that he is to resign just two months into the job.

Sir Peter has been at the Prime Minister’s side throughout his time in office, both at home and abroad. The reasons for his departure were unclear last night. The 57 year old – who was formerly head of the Foreign and Commonwealth office – had been expected to stay in the post well into next year.

The news has presented a headache for the Prime Minister who has made the post a hallmark of his new approach to dealing with national security concerns, including the war in Afghanistan.

Update: Press Association has this:

“He is not leaving his post early,” a spokeswoman for the Prime Minister said. “It was always the understanding that he would do it for a limited period.”

Sir Peter, who was previously permanent undersecretary at the Foreign Office, is expected to depart in the second half of 2011.

There is speculation that he could take over as ambassador in Paris. But officials stressed no decision had been taken over his destination, or on the identity of his successor.