The former lead civil servant at the Foreign Office, sacked by the prime minister and foreign secretary last week, will give his side of the story in Parliament this morning.

Sir Olly Robbins, who had been the permanent under secretary at the Foreign Office since January 2025, was removed from his post last Thursday evening after the prime minister discovered he had not been told by Sir Olly that Lord Peter Mandelson had failed his vetting process to be the UK's ambassador in Washington.

Sir Olly is expected to defend his decision not to tell Sir Keir Starmer and is understood to be bruised and upset at both losing his job and the loud, repeated and personal criticisms of his conduct.

A friend of Sir Olly told the BBC, in apparent contrast with how he feels he has been treated: "Olly doesn't do personal. He never has and he never will."

He is likely to set out to the Foreign Affairs Committee the context in which his initial decision was taken – that Lord Mandelson's appointment as ambassador had already been publicly announced and his interpretation of the law, the Constitutional Reform and Governance Act, 2010, was that he was not authorised to share the conclusions of the UK Security Vetting process.

The prime minister's allies maintain this morning, as Sir Keir set out in the House of Commons on Monday, that their interpretation of the law is very different and Sir Olly could and should have shared that information with ministers.

Supporters of Sir Keir struggle to understand why Sir Olly, having initially decided against sharing the information, remained of that view after Lord Mandelson's sacking and when questions returned about the process surrounding his appointment.

The chair of the Foreign Affairs Select Committee, Dame Emily Thornberry, is furious with Sir Olly for failing to disclose what he knew to the committee when they asked specifically about Lord Mandelson's vetting.

A key question in advance of the committee's questioning is whether Sir Olly acknowledges sharing what he knew with anyone else and, if so, who and what it was he chose to tell them and not tell them.

The prime minister will hope the former senior civil servant's testimony will strengthen their argument that there were repeated opportunities for him to be informed and these were not taken.

After the committee's session with Sir Olly, there will be another debate on the issue in the Commons, secured by the Conservatives.

Reflecting last night on suggestions the entire British state was being brought to bear against Sir Olly, an ally said: "That's exactly how it feels."