ATHENS — Two flags can be seen fluttering above the rooftop of the British Embassy in the Greek capital: a Union Jack and the blue and yellow standard of Ukraine.  No similar pairing is visible at other embassies nearby. 

While as a whole the West “has contributed importantly to a splendid Ukrainian victory in the first phase” of Russia’s war on the country, as Conrad Black writes in today’s New York Sun, the tenacity of Britain’s support stands out — and, to Vladimir Putin’s eminent dismay, does not look set to diminish even as the war heats up in the east.

It almost goes without saying that bipartisan American military assistance has been and will continue to be a crucial factor in helping Ukraine’s military in its ongoing struggle to rout the invading Russian forces. But among European players in this nasty and unnecessary conflict, one country stands head and shoulders above the rest both in terms of recognizing what is at stake if Mr. Putin’s gambit succeeds and in doing every bit it can to stop him. That is Britain. 

At a moment when Germany has waffled on arms deliveries to Kyiv and the French president’s effort to pacify Mr. Putin via telephone has fizzled, more facts are emerging about just how vital British assistance has been in clipping the Kremlin’s wings. 

According to the Daily Telegraph, the British prime minister backed his defense secretary, Ben Wallace, against voices in Whitehall by provisioning Ukraine with vital weaponry in the nick of time to stop the Russian armor and defend the Hostomel air base, which in that newspaper’s estimation “marked the end of Putin’s blitzkrieg.”

That is a claim substantiated by weeks of reports, prior to the Russian retreat from the areas around the Ukrainian capital at the end of March, about how the hotly contested, highly strategic airport at Hostomel was trading hands between Russian forces and the Ukrainian military. 

Had the Ukrainians not prevailed, the Telegraph asks, “would the Russians have taken Kyiv, as the Germans took Paris?” A Ukrainian may have already provided the answer: The head of the Kyiv regional police force, Andriy Nebitov, has said that Ukrainian soldiers broke through Russian positions at Hostomel after conducting their own artillery strikes, disrupting the Russians’ plan to attack Kyiv directly. By mid-March the Russians had retreated from Hostomel. 

Prime Minister Johnson has also put his own boots on the ground, so to speak, when he made a surprise visit to  Kyiv to meet with the Ukrainian president earlier this month. Even the left-of-center Guardian newspaper had to admit that “Johnson’s Kyiv visit achieved little but was a symbolic win” for the prime minister and President Zelensky.  

Downing Street has already allocated upward of $600 million worth of military aid to Ukraine, including more than 800 NLAW anti-tank missiles, Javelin anti-tank missiles, Starstreak air defense systems, and more. 

Perhaps that is what raised the hackles of Kremlin-backed news agency RIA Novosti, which ran a headline to the effect: “London admits it is at war with Russia in Ukraine.” 

That article cites a report from the Times of London according to which, as the Russian news agency has it, the British special forces service is training members of the Kyiv Territorial Defense Force. For the Russians, this is “de facto recognizing that the current British army is directly involved in the military conflict.”

If it is, so what? Britain is a nation that will be cowed by none, and not just on the battlefield. It sanctioned implausible peacemaker Roman Abramovich, the Russian oligarch widely seen as a financial henchman for strongman Vladimir Putin, before the European Union did. Mr. Abramovich is banned from entering the United Kingdom, sealing his fate as a pariah only slightly less reviled than Mr. Putin himself. 

Furthermore, Britain yesterday revoked the Moscow Stock Exchange’s status as a recognized exchange. The move by Her Majesty’s Revenue & Customs effectively cuts off U.K. tax benefits for investors who may in the future attempt to trade stock in Moscow. 

The resilience of the highly motivated Ukrainian armed forces, as the British Ministry of Defense describes the outnumbered fighters, will of course be on display on the frontlines as the Battle for Donbas, as Mr. Zelensky has termed it, unfolds. But if Britain had a decisive, albeit behind-the-scenes role in helping to eject Russia from western Ukraine, look for similar preventative action to happen, quietly and more slowly, in the east.

As for the reliably unflappable Mr. Johnson, he is not one to rest on his laurels or anyone else’s, for that matter. While pledging additional artillery support to Ukraine, the prime minister told the House of Commons today, “The urgency is even greater now because Putin has regrouped his forces and launched a new offensive in the Donbas. We knew this danger would come.”