"Engage but beware", Theresa May warned of Vladimir Putin in her speech to the Republicans earlier this year. Donald Trump has since had cause to recall her advice. His dalliance with the Russian president has cost him a national security adviser (Michael Flynn) and damaged his domestic standing. Last week's strike on Syria was partly motivated by a desire to distance himself from Putin, Bashar Al-Assad's greatest patron. "He [Trump] is not a guy who gets intimidated," the president's son Eric boasted. "I can tell you he is tough and he won’t be pushed around."

But though the US launched the attack, it is the UK that has led the push for new sanctions against Russia. Having initially refused to endorse Boris Johnson's plan to target Russian military officials, No.10 last night declared that there was a "window of opportunity" to "persuade Russia that its alliance with Assad is no longer in its strategic interest." The statement, which followed a 20-minute phone call between May and Trump, contrasted with that issued by the White House, which made no mention of Russia. Though the US has endorsed Johnson's sanctions plan, doubts remain over the extent to which Trump is prepared to intensify his breach with Putin.

G7 foreign ministers, who are meeting in Lucca, Italy, have today rejected the UK-US proposal, with Germany, France and Italy all demanding that a prior investigation into last week's chemical weapons attack. Not for the first time, Britain has been in the anti-Putin vanguard, prompting Jeremy Corbyn to yesterday accuse Johnson of a "Cold War mentality".

Since May entered No.10, policy has been toughened in multiple areas. Last autumn, the UK deployed 800 troops and long-range missiles to Estonia as a deterrent to Russian revanchism. In strikingly blunt terms, May condemned the country's "sickening atrocities" in Aleppo and urged the west to "keep up the pressure" on Putin.

The government is also targeting forces beyond the Kremlin. The Home Office has accepted an amendment to the Criminal Finances Bill allowing British authorities to freeze the assets of Russians convicted of offences under the Human Rights Act. Hedge Fund Boss Bill Browder, who complained that a "welcome mat" had been put out for "criminal money" in London, said of the UK's new stance: "There's definitely a change in attitude from Theresa May's government, which seems to be more robust than David Cameron's." May has barred Putin-aligned oligarchs from Conservative fundraising events (in contrast to her predecessor) and has encouraged MPs not to attend Anglo-Russian parliamentary groups on the grounds that they are a security risk.

In a new era of Russian adventurism, Britain is emerging as Putin's most persistent foe. At the end of last year, the UK appeared increasingly isolated as Trump courted the Kremlin and the pro-Russia François Fillon threatended to win the French presidency. But the US's tougher stance and Fillon's political woes have reduced the risk of a calamitously divided west. Though the epic task of Brexit will constrain the UK's influence, Putin now knows that he cannot hope for a softer line from May.