One of Europe’s few true friends of Israel, Boris Johnson, is sounding an alarm on reports that police at London’s Heathrow Airport are questioning passengers about events in Israel and the “Palestinian territories” — and he has without missing a beat accused Scotland Yard of “playing politics.”

The prospect of British police officers interrogating arriving passengers at Britain’s biggest airport about events in the distant Middle East may strike some travelers as intimidating and others as ludicrous. It is a small world, though, and altered states of international travel aside, the Gaza contagion has already felled a rising star of the Conservative Party once seen as potential rival to the faltering prime minister, Rishi Sunak. 

What has raised Mr. Johnson’s hackles is the appearance at Heathrow of posters placed by the Metropolitan Police headlined, “Travelers who have been in Israel/Palestinian Territories,” with the following text — in Arabic, English, and Hebrew — underneath: “If you have been in Israel/Palestinian Territories and have witnessed or been a victim of terrorism, war crimes or crimes against humanity, then you can report this to the UK police.”

Additional wording on the posters states that “UK policing is supporting the work of the International Criminal Court, which is investigating alleged war crimes in Israel and Palestine from June 2014 onwards. Any evidence gathered may be shared with the ICC in support of their investigation.”

Scotland Yard, which is the headquarters of London’s esteemed Metropolitan Police, confirmed on Wednesday that it has already received more than 40 reports, with the vast majority of these, the Telegraph first reported, being allegations of war crimes against Israel. 

On Wednesday, Mr. Johnson told that newspaper that he was concerned about “the worrying politicization of the Met Police.” Scotland Yard, for its part, says it has a “responsibility to support” the ICC and cited “higher volumes” of British nationals returning to the United Kingdom since Hamas started the war last October.

If British Jews, most of whom already conceal their Jewish identities in public due to widespread antisemitism, have cause to be piqued by this peculiarly one-sided politicization, so too does one very prominent Briton who happens to be Hindu: Prime Minister Sunak. 

Mr. Sunak’s popularity, for one thing, is in freefall. The cover of this week’s Private Eye, the British satirical magazine, sums up the state of affairs thusly: “Merry Rishimess.” Elsewhere it adds, “I blame the Ho, Ho, Home Secretary.” Certainly the current home secretary, James Cleverly, has had his fair share of gaffes since he assumed office last November, and these come with a political cost. The “Rishimess,” though, started, in effect, when Mr. Cleverly’s predecessor, Suella Braverman, waded into the Gaza fray. 

Last November, Ms. Braverman referred to pro-Palestinian protesters as “hate marchers,” as doubtless many of them were. Others were violent and remain at large. In any case, Mr. Sunak responded by firing her — a decision that an influential Tory backbencher, Jacob Rees-Mogg, called “a mistake, because Suella understood what the British voter thought and was trying to do something about it.”

How will Mr. Sunak respond to the ugly sight of British airports turning into echo chambers for the kind of pervasive anti-Israeli invective infecting Europe that would be nice to shrug off as simply tiresome were it not so patently dangerous? If the situation with Ms. Braverman is any guide, he will do nothing. 

In that respect is Mr. Johnson, whose premiership Mr. Sunak had no small role in undoing, nursing new designs on Downing Street — possibly even before a general election that is likely to be held later this year? Mr. Sunak has already plucked one prominent member of his cabinet, the foreign secretary, David Cameron, from past governments. Wouldn’t offering his embattled top spot to the man he unseated be a nifty feat?

That is no doubt wishful thinking. What he should be doing concretely, many would say, is self-evident — to tell Scotland Yard to stop fixating on the World Court at the Hague and focus on London, where rising crime poses a threat to residents and tourists alike.

That would take strength of conviction the ever-grinning premier appears to be lacking. As to where opposition leader Keir Starmer stands in all this — well, does it even matter? Not yet. More deft maneuvering by Mr. Johnson means that a year from now, it could matter even less.