UK Prime Minister Sir Keir Starmer faces intense pressure as he prepares to explain in Parliament how Lord Peter Mandelson became ambassador to the US despite failing security vetting. The Downing Street veteran will reject calls to resign today, blaming sacked Foreign Office head Sir Olly Robbins for the "unforgivable" act of not disclosing the vetting failure.

Robbins, expected to testify tomorrow, maintains he addressed red flags through mitigations for Mandelson's conflicts of interest. The scandal has created a rift between senior officials and raises questions about the government's security protocols during a sensitive US-UK relationship period.

The fallout threatens Starmer's leadership just before May's local elections, with some Labour MPs suggesting significant losses could trigger his departure from office. The prime minister's ability to weather this political storm will likely determine his party's electoral prospects and his own future in British politics.