Cabinet secretary apparently advised Starmer to wait for vetting before appointing Mandelson

The then cabinet secretary, Simon Case, appeared to advise Keir Starmer to complete security vetting for Peter Mandelson before announcing an appointment, documents reveal.

The documents released last month by the Cabinet Office as part of the disclosures over the US ambassadorial appointment also show Mandelson was offered a “higher tiers” briefing before his vetting was finalised.

The Guardian revealed last week that Mandelson failed his initial vetting by United Kingdom Security Vetting (UKSV) and that decision was then overruled by the Foreign Office. He was appointed as US ambassador but sacked in September after new disclosures about his friendship with the late child sex offender Jeffrey Epstein.

In a letter written by Case to the prime minister, he is advised that in order to give the Washington role to a political appointee, the FCDO would “develop a plan for them to acquire the necessary security clearances and do due diligence on any potential conflicts of interest or other issues of which you should be aware before confirming your choice”.

The letter, sent on 11 November 2024, said the decision would then be formalised by the foreign secretary in a letter to the FCDO. Mandelson’s appointment was announced by No 10 just over a month later, on 20 December.

The documents also show Mandelson was offered a “higher tiers” briefing on 6 January, before his developed vetting was confirmed on 29 January. This means he was offered highly classified briefing from the FCDO as US ambassador before he finished the formal vetting process, one he is now known to have failed before that outcome was overruled by the Foreign Office.

Starmer will deliver a high-stakes statement to MPs on Monday where he will set out how Mandelson was able to take up his role as UK ambassador without the Foreign Office revealing it had overruled the decision to fail his vetting.

The scandal has already led to the sacking of the top civil servant at the Foreign Office, Olly Robbins, who is expected to appear before MPs on Tuesday in what could be another moment of grave peril for Starmer.

In Case’s original letter to Starmer, he suggests political appointments are rare, giving examples of Ed Llewellyn, David Cameron’s former chief of staff who was appointed ambassador to France.

Downing Street has strongly disputed claims by allies of Robbins that he was prevented by law from telling ministers Mandelson had failed vetting, arguing that there was a difference between being involved in the decision and being informed about it.