A high-level British inquiry into the killing in London in 2006 of Alexander Litvinenko, a former KGB officer turned critic of the Kremlin, has not only established that the Russian state was involved, but that a link could probably be traced to Vladimir Putin himself. That home secretary Theresa May has reacted by describing the murder as a “blatant, unacceptable, breach of the fundamental tenets of international law” is welcome – but not enough. The assassination of Litvinenko has now been officially established as “a state-sponsored act”, with a “strong probability” that the killers acted “under the direct order” of the Russian FSB secret service, in an operation “probably approved” by the Russian president. Yet the UK has made plain that diplomatic relations with Russia will not be affected. True, Mrs May announced that a European arrest warrant would be sought against the two Russian agents who poisoned Litvinenko with polonium in a London hotel, but if only on the strength of the home secretary’s own muscular language – pointing the finger at the upper echelons of the Russian regime – this, surely, cannot be enough.

The report’s credibility is not in doubt. The tireless commitment shown by Litvinenko’s widow, Marina, has successfully drawn a bright, unsparing light on this murder. The crime ranks as the first independently documented assassination of a Russian dissident by the Russian state on European soil, and – another nasty first – using nuclear substances to boot. One needs to go back to the 1978 killing of the Bulgarian dissident Georgi Markov, poisoned with the ricin-filled umbrella tip on Waterloo Bridge, to find anything comparable.

Insisting there should be no diplomatic fallout amounts to an admission that Britain can be cowed. The claimed constraints – especially the need for cooperation in the Middle East – are not especially convincing. Russia’s policies in Syria have, by aiding the Assad regime, contributed to strengthening Islamic State rather than defeating it. If Russia decides to sideline Assad one day, that will only happen because of Moscow’s own strategic calculations, and not because of Britain dialling down its response to the Litvinenko murder. The same applies to the Iran nuclear deal, or Ukraine: to say a strong British reaction will derail international diplomacy is to overstate British influence. On the contrary, putting some pressure on senior Russian officials would enhance British credibility. London only gave the inquiry full support after Russia attacked Ukraine. Clearing up the lingering impression that the British court system might somehow be negotiated with will now require a tough stand.

The most efficient way to follow up on the report would involve Europeanising the issue. After all, the Litvinenko assassination concerns all European democracies, not just Britain. Russian political opponents don’t just live in London, nor can the reach of Russian agents ordered to eliminate dissidents overseas be considered limited to British territory. On the basis of the report, European governments should work towards a common sanctions list, targeting, by name, the Russian officials linked to criminal activity and human rights abuses.

There is a precedent for this, in the US. In 2012, the Obama administration enacted the Sergei Magnitsky Act, which led to asset freezes and visa bans for 30 Russian officials who had been complicit in the death of a crusading Russian lawyer while in jail on trumped-up corruption charges. Several European parliament resolutions have called for similar EU measures. The Litvinenko report is an opportunity to do just that.

It is a chance to focus on all the individual responsibilities that have been exposed, including those of such close Putin allies as Nikolai Patrushev and Viktor Ivanov – whose names are mentioned in a report that, naturally, they have called a sham. Nothing will make Russian officials pay attention like being banned from the European mansions and resorts that they enjoy visiting, or being blocked from accessing the money they have stashed in European banks. Mrs May is right to say any measures against Mr Putin himself would come up against a head of state’s immunity. And there is little chance of any international justice mechanism moving against Mr Putin even after he leaves office – for this assassination or for other crimes. But even if a rerun of the Pinochet case is unlikely, it is precisely because this case encapsulates the darker side of Putinism that stronger measures, and at a European level, are now required.