Theresa May has to be tough now. The heinous attack against a Russian-born naturalized citizen and his daughter on British soil has caused public outrage. The chemical warfare agent that was used has now been identified as a Russian-produced super poison; Russian President Vladimir Putin is suspected of having at least sanctioned the attack on former double agent Sergei Skripal, if not personally ordering it himself. The British government finds itself suspended between anger and helplessness.

Theresa May and the lack of credibility

When another Russian ex-spy and Kremlin critic – Alexander Litvinenko – was assassinated in 2006, Theresa May was still Minister of the Interior. She endlessly dragged out the case just to avoid messing with Moscow. It took nearly a decade to determine the Kremlin's involvement in the murder.

Since then, there have been at least a dozen other suspicious deaths of Russian citizens in the UK, all classified as coincidences and downplayed by the government. But that response should be over now. May is now under enormous pressure from her own party to react with appropriate harshness to Moscow's provocations. And the prime minister somehow needs to restore her credibility.

"Little Moscow" on the Thames

The UK has created the basis for its current problems with Putin. After the collapse of the Soviet Union, it opened its doors to the Russian robber barons, as long as they brought enough money. In their wake came dissidents, active and former spies, and dodgy profiteers. "Little Moscow" on the Thames became a huge money laundering machine and the British capital benefited from the newly rich Russians.

Meanwhile, the "Russian Connection" has long arrived in the establishment. A former Putin confidant bought a British newspaper; the Conservatives have received almost a million individual political party contributions from Russian citizens in recent years. And Russia Today's broadcasts are teeming with British opposition politicians.

Read more: What you need to know about the Russian presidential election

DW's Barbara Wesel

A British counterstrike?

The prime minister must take the helm if she now wants to show the Kremlin firmness and determination. In the meantime, London has created a kind of threatening backdrop, ranging from the expulsion of diplomats, i.e. spies, the freezing of oligarchs' funds, the shutdown of the Russian channel "Russia Today" to the so-called "nuclear option" – kicking Russia out of the football World Cup this summer.

But even this counterattack, which would certainly hit Putin hardest, would be effective only if all Europeans participate. And up to now, nobody has shown any inclination for this. The same applies to further sanctions: if London imposes them alone, they remain largely laughable.

At the Munich Security Conference a few weeks ago, Theresa May spoke in moving words, summoning a new security partnership after Brexit. But the reaction from the European Union remained subdued. The EU has little desire to recognize future cooperation with the British as a card in Brexit poker.

Another ally bites the dust

In the wake of the attack, the now former US Secretary of State Rex Tillerson had harshly condemned the crime and offered strong words of support to the British PM – perhaps even strong enough to cost him his job, or so it is speculated.

The EU also did not lack strong words and declared solidarity with the UK, its member state. And indeed, the British government can formally rely on the support of its partners in Brussels for another year. Political capital, however, is something May no longer holds in the EU. The road to Brexit inevitably leads to the UK's departure from the bloc in a year. Behind the scenes, there is currently little inclination to go along with tighter sanctions against Russia as a favor to London.

Theresa May is now learning what it's like to live alone at home. And this is not a good time to be internationally isolated. US President Donald Trump's trade war and a hardened foreign policy in Washington do not bode well for Europe. Perhaps this is one aspect of the cost of Brexit that the prime minister had failed to adequately consider before.