Sir Keir Starmer faces not one but two judgment days next week as he battles to save his job, while his ‘angry’ sacked Foreign Office boss is set to stick the knife in as he launches his own staunch defence. 

The Prime Minister will appear before MPs on Monday ahead of Sir Olly Robbins’s own Parliament appearance the next day to explain his department’s role in Lord Mandelson’s failed security clearance. 

The PM has blamed Sir Olly for not informing Number 10 that Mandelson had failed security vetting. His opponents say it is incredible that he did not know or make it his business to know in light of the peer’s known connection to sex offender Jeffrey Epstein. 

Meanwhile the increasingly hostile war of words which has broken out between Number 10 and the Foreign Office about who knew what when about the disgraced former US ambassador and why he was still appointed to the Washington role continued to ramp up. 

Sir Olly’s predecessor at the Foreign Office publicly backed him today following his sacking on Thursday saying he was simply ‘following the rules’ and accused the Prime Minister of ‘throwing him under the bus’. 

Criticising the PM as ‘wrong’, Lord Simon McDonald accused Number 10 of ‘wanting a scalp as quickly as possible within the news cycle’ and not even giving Sir Olly, who he says was following legal process, the chance to give his own side of the story. 

He also suggested that the decision to appoint Mandelson had already been made and that the Prime Minister ‘wanted his man’ in Washington and it was ‘an interpretation’ that the Foreign Office was effectively left to make it work. 

He also warned in stark terms that the Foreign Office was now facing ‘its biggest crisis’ in more than four decades and needed a new Head ‘as quickly as possible’.

‘This story broke on Thursday morning and within the news cycle, Olly Robbins had been required to resign which shows to me that Number 10 wanted a scalp and they wanted it quickly. 

'I cannot see that there was any process, any fairness, any giving him the chance to set out his case and that feels to me wrong,’ he told the BBC.

His comments came as it emerged that Sir Olly was said by friends to be ‘very angry’ and likely to appear before the Foreign Affairs Committee on Tuesday to defend himself although he has apparently not yet officially accepted the invitation.

This means that even if the Prime Minister survives a likely mauling in the House on Monday when he attempts to explain his own apparent ignorance of Mandelson’s failed security vetting, he could face a further reckoning on Tuesday.

Lord McDonald, who joined the Foreign and Commonwealth Office in 1982 and was in charge between 2015 and 2020, insisted that security vetting was a ‘confidential process’ and that unless failure was ‘a black and white issue’, it would be bound by legal rules set out in the CRAG Act (Constitutional Reform and Governance) in 2010.

Asked by BBC Radio 4’s Today programme whether the ‘bought’ the government’s position, he said: ‘No, I do not. That position misunderstands and misrepresents the system. Security vetting is a key part of the system. It is a confidential process.

‘There is a report and generally the details of that report are very closely held and they would never be shared with the Number 10 or the Prime Minister and generally when things are confused and sensitive it is a matter of judgment and mitigation and it feels to me like we are in that grey area rather than in a very black and white world which Number 10 want.’

Asked whether an official was bound to report details of a security vetting failure to the PM or Number 10, he said: ‘These things tend to be a bit murkier. The security vetting will have incomplete information. They might be unhappy about one to two details and there might be mitigations to be put in place and that all happens quite regularly but it doesn’t amount to failure.

‘If there had been a failure then that fact would have to be conveyed to the political level but the fact that it was not indicates to me that the picture was more complicated than Number 10 wishes to present.’

Lord McDonald said it was this requirement for confidentiality for those in charge of the vetting process which meant Sir Olly ‘maintained confidence’ when he appeared before Emily Thornberry’s Foreign Affairs Committee last year. 

‘He wouldn’t go into detail because this is a confidential process. The end result is shared but all the workings behind it remain confidential.’

Asked to explain the reason for such confidentiality which might seem astonishing to the public, he said: ‘The process was set out in law and the top official at the Foreign Office was observing process according to law and this is a confidential process like medical records are confidential.

‘Certain things have detail which is not shared at all and this is in that category. What I do know is that it tends to be complicated in this kind of sensitive setting and there is judgment involved and so he was following the rules and applying his judgment as far as I can see.'

The former top mandarin, who sits in the Lords as a Life Peer and is also Master of Christ’s College, Cambridge, suggested that the Foreign Office was presented with a fait accompli over Mandelson’s appointment.