Was this an inexcusable failure or standard practice?

A fairly key question. Downing Street is clear: it is “staggering” that Mandelson failed vetting, and that the Foreign Office not only overruled this but told no one in No 10.

However, Ciaran Martin, a former top civil servant with past involvement in vetting work – and a close friend of the ousted Olly Robbins – said this was an oversimplification. Rather than vetting being a simple yes or no, he told the BBC, it was a balance of risks, and entirely standard for officials to decide whether this was acceptable.

Did Starmer mislead parliament, even unintentionally?

The prime minister told MPs that “full due process” had been followed in appointing Mandelson.

Asked if parliament had been misled, even if this was not the PM’s fault, No 10 appeared to accept this was possible, saying: “The prime minister feels that he should update parliament on Monday on the basis that parliament should have known about this and should now know about this.” That is not a “no”.

Should Downing Street have known earlier?

The perhaps obvious answer is: well, yes. But if you accept the idea of a No 10 operation kept entirely in the dark by its own Foreign Office, then even here there are elements to be questioned, such as the emergence of a journalist’s question to Downing Street’s then head of press in September last year asking about sources saying Mandelson did not clear vetting.

Did No 10 check this? Its version is that officials “repeatedly asked for the facts of the case” but were simply not told.

Will Starmer have all the answers next week?

This remains uncertain. The prime minister is scheduled to address MPs in the Commons on Monday afternoon, and there will be no shortage of questions, not least from the various opposition party leaders who have already called on him to resign.

As far as can be ascertained, Downing Street is confident enough of the basic facts of the case to have asked Robbins, who was the head civil servant in the Foreign Office, to resign on Thursday night.

But at the same time, a full and formal investigation into what happened, and why, has not yet begun, so we can expect Starmer to, when necessary, hide behind the need to wait for fuller information.

Was this ultimately all Downing Street’s fault?

This is as much a political question as anything else. But there is a plausible case for believing that the Foreign Office decided to overrule the worries about Mandelson for one very simple reason: Starmer had already named him as ambassador to Washington.

The UK already had someone very capable in the job, in career diplomat Karen Pierce, but the advent of a second Donald Trump presidency saw No 10 hit on the idea of a high-profile political appointee, one seen as able to navigate the murky waters of a Trump White House.

Given this decision was taken at the very top, it would have been a difficult moment for the Foreign Office to call No 10 and say: “Sorry, you’ll have to think again.” So, were they effectively bounced into it? No 10 says Starmer had no clue that vetting could be overruled, and so cannot be blamed. Others may think differently.