David Cameron suffered his first Conservative resignation from the Government last night, when Baroness Neville-Jones quit as Security Minister. A former chairman of the Joint Intelligence Committee, the Baroness had been appointed to the Conservative frontbench four years ago.
She was believed to have been unhappy at failing to secure a Cabinet seat after the general election, instead of the minister of state post with responsibility for security and counterterrorism.
She was also reported to have been passed over by Mr Cameron for the post of the Government's National Security Adviser.
In a letter to the Prime Minister, Lady Neville-Jones said: "As you know, I told you a few months ago that I thought the time was approaching to do this."
She promised that she would "continue to give the Government, the Conservative party and your leadership strong support".
In his reply, Mr Cameron praised her for drawing up the original plans for the National Security Council, which he chairs.
She was replaced immediately by the former Conservative MP Baroness Browning of Whimple.
Lady Neville-Jones, 71, was a career diplomat, whose postings included the former Rhodesia, Washington and Brussels, before returning to work in the Cabinet Office. She served as JIC chairman in 1993 and 1994 and was also a governor of the BBC. She has been appointed special Representative to Business on Cyber Security.