Keir Starmer will address the Commons today on the Peter Mandelson vetting scandal, after being told he must finally take responsibility and stop blaming others. 

The Prime Minister faces accusations of breaking the Ministerial Code by failing to promptly inform the Commons that new evidence had cast doubt on his earlier assurances that 'full due process' had been followed in appointing the US ambassador. 

Sir Keir begins a make-or-break week for his faltering premiership as he answers to angry MPs over his role in what has been described as a 'tawdry and shaming' affair. 

He has already faced calls to resign from Labour backbenchers and peers, as well as opposition party leaders, over what they labelled 'catastrophic' misjudgments. 

However Sir Keir signalled he would not accept the blame, saying last night he would make it 'crystal clear' to MPs that he was kept in the dark.  

Martin Beckford says these are the questions MPs will want answered:

1. Did Sir Keir mislead Parliament?

The Prime Minister told MPs on several occasions that 'full due process' was followed, including 'security vetting', before Mandelson took up his role. 

His right-hand man Darren Jones insisted last week this was technically correct because the Foreign Office had a little-known power to overrule vetting concerns. 

But Sir Keir will face damaging accusations that he did not tell the truth, regardless or whether he knew the full facts at the time.

2. Why didn't the PM correct the record immediately?

The Ministerial Code requires members of the Government to correct 'any inadvertent error at the earliest opportunity' if they did not give accurate information to MPs. 

Sir Keir was told about the vetting scandal on Tuesday night so will be asked why he didn't correct the record on Wednesday, before Prime Minister's Questions.

3. Was Sir Keir really the last to know?

Cabinet Office Permanent Secretary Cat Little was handed a document revealing the vetting failure in late March and discussed it with the country's top civil servant, Dame Antonia Romeo. 

The PM was told weeks later. Sir Keir will be asked if he is happy that they kept him in the dark – and how many others in No 10 knew before him.

4. Should he have been told what had happened?

Foreign Office mandarin Sir Olly Robbins, who made the fateful decision to give Mandelson the job, believes he was not allowed to tell anyone about the concerns that emerged during the vetting process. 

But many who have worked in Whitehall say they had been informed when the alarm had previously been raised over other candidates.

5. Why did officials say Mandelson should not get security clearance?

Although the New Labour grandee has been linked to Russia and China as well as paedophile Jeffrey Epstein during his long and colourful career, it is not yet known what exactly led UK Security Vetting officials to raise the red flag over his appointment to Washington.

6. Has the PM seen the verdict himself yet?

Last month No 10 officials finally got hold of the document revealing that 'the recommendation from the vetting officer had been that developed vetting should not be granted to Peter Mandelson'. 

But Sir Keir may have been told that the reasons behind the advice have to remain secret to protect Mandelson's privacy.

7. Did Mandelson read top-secret reports?

As well as developed vetting, Mandelson needed another type of clearance known as STRAP so he could be shown intelligence material. 

Did he gain this despite failing the checks, or was he allowed to see the top-secret files anyway?

8. How much digging did Downing Street do?

Journalists went to No 10 as early as September with claims that Mandelson had failed his vetting but were assured that the normal process had been followed. 

Downing Street has insisted that officials had repeatedly asked questions of the Foreign Office about the process, but it is not known exactly what they asked or what responses they received.

9. Why didn't Foreign Secretary know?

David Lammy, in charge of the Foreign Office at the time, revealed yesterday he heard about the debacle only last Thursday. 

But Tory predecessor Sir James Cleverly said it should have been his job to find out.

10. Was the 'fall guy' only obeying orders?

Sir Olly, who was sacked by Sir Keir last week, told MPs in November: 'It was clear that the Prime Minister wanted to make this appointment himself.' 

Did the PM or his then chief of staff Morgan McSweeney make it known that their candidate had to be put in place regardless of any concerns raised?