SIR KEIR STARMER would have blocked the appointment of Peter Mandelson as US ambassador had he known that the New Labour schemer — twice sacked from Tony Blair’s cabinet for his dubious dealings — had failed security vetting, ministers insisted today.

Technology Secretary Liz Kendall and Deputy Prime Minister David Lammy defended the Prime Minister ahead of his appearance before MPs on Monday.

Lord Mandelson took the job of ambassador in January 2025 but was sacked in September after details of his continued association with the paedophile US financier Jeffrey Epstein emerged.

Last week the Guardian reported that Lord Mandelson had been appointed after the Foreign Office overruled a recommendation not to grant him special security clearance.

The department’s chief civil servant, Sir Olly Robbins, was sacked on Thursday after ministers blamed him for not telling Sir Keir about the vetting failure.

But former shadow chancellor John McDonnell MP suggested it was Downing Street aides who had kept the Prime Minister in the dark, telling Channel 4 News on Saturday: “The issue for me was: who was in control of the process?

“If Olly Robbins has overridden the vetting process, what pressure was he under and who was exerting that pressure? Because it looks suspicious, it might well be those around No 10.”

Asked who he meant, he pointed the finger at Sir Keir’s disgraced Downing Street supremo — and Lord Mandelson’s political protege — Morgan McSweeney.

The former No 10 chief aide was sacked for his key role in Lord Mandelson’s appointment despite his publicly documented Epstein links.

Mr McSweeney failed to alert police to the fact that he was Downing Street chief of staff and gave the wrong location when he reported his phone stolen in October; the alleged theft means that key messages between him and Lord Mandelson may not be aired.

Mr Lammy told the Guardian that he had “absolutely no doubt at all” that the PM minister “would never, ever, have appointed” Lord Mandelson if he had known he failed vetting and Ms Kendall echoed his comments on the BBC today.

In February, Sir Keir told the Commons that vetting gave Lord Mandelson clearance and that “full due process” had been followed.

Last week a Downing Street memo came to light revealing that two senior civil servants had learned of a “discrepancy” in Lord Mandelson’s vetting.

Asked why Sir Keir was not losing his job, Ms Kendall replied: “Because the Prime Minister, on the big calls facing this country, has made the right calls.”