One by one, European leaders publicly expressed their support for Ukraine in the hours immediately following those shocking White House exchanges between Presidents Donald Trump and Volodymyr Zelensky.

The prime minister, however, said nothing.

My phone then went off as I hurried into the studio for BBC News at ten.

According to a statement I received from No. 10, the prime minister “retains unwavering support for Ukraine and is doing all he can to find a path forward to a lasting peace” after speaking with both of them.

In addition to completely upending the relationship between America and Ukraine, two allies, in the most spectacular way possible, Friday afternoon in the White House also upended recent diplomacy due to the visits of French President Emmanuel Macron and the Prime Minister.

The warmth and camaraderie between Trump and Sir Keir, which I had witnessed in the same room just 24 hours prior to Volodymyr Zelensky’s visit to the Oval Office, was a stark contrast to what was about to happen.

Like Emmanuel Macron before him, Sir Keir had tried to curry favor with the highly unpredictable American president because he believed it was the sensible thing to do.

The prime minister now has to deal with a situation in which two of the UK’s allies are at odds in the most blatant and irate manner possible.

The specifics of the two phone calls Sir Keir made on Friday night are unknown, according to sources, who are acutely aware of how sensitive this delicate situation is.

However, those calls were at least made possible by the UK’s diplomatic efforts in recent weeks, which allowed the UK to try to serve as a link between Washington and Europe as well as between Kyiv and Washington.

However, there is a political price for it. The Scottish National Party and other domestic opponents of the government contend that Donald Trump’s invitation to make a second state visit to the UK ought to be withdrawn.

Already, Sunday’s European leaders’ summit in London, which the prime minister hosted and which President Zelensky attended, was looking increasingly important. Now, it has become even more significant.

The scenes in the Oval Office were “deeply troubling and sobering,” but they also showed “in the starkest possible terms” how much “the world we’ve all experienced for the last 80 years” had changed. Trade Minister Douglas Alexander explained this to BBC Radio 4’s Any Questions, saying that we were in “uncharted waters.”

The “bravest political leader in Europe since Winston Churchill” is another term he used to describe President Zelensky.

Additionally, Kaja Kallas, the top diplomat for the European Union, stated that it had “become clear that the free world needs a new leader.” It is our responsibility as Europeans to accept this challenge.

But that’s the main point here. Could Europe do that?

The White House must give Ukraine a security guarantee as part of any peace agreement, according to the UK and other countries’ requests to the US.

That is what the UK wants to be considered air cover. Given the risk of a worsening conflict with Russia, this would be a significant request of any president at any time.

However, it is a huge request from a president who has made it clear that he has absolutely no interest in American military expeditions abroad.

Thus, President Zelensky will be joining his European allies in the UK this weekend.

The amount at stake is enormous.