What can Britain do to Russia?

The government of Theresa May has a tricky problem ahead. No, not Brexit this time. What will happen next if prima facie proof is found of Kremlin involvement in the nerve agent attack on double agent Sergei Skripal and Yulia, his daughter? So far one possible threatened response sounds embarrassingly weak: stopping UK VIPs from attending the football World Cup due to take place in Russia in the summer. Boris Johnson, the Foreign Secretary, and Amber Rudd, the Home Secretary, have both pledged to take appropriate and robust action against anyone involved in the dastardly attack in Salisbury, whoever it is and wherever they are. Well, of course they must say that. But in reality, if the evidence-chasing pinpoints the blame on the Russian government, it is difficult to see what the UK government can do that would significantly punish Putin and co. Putin will deny any knowledge or involvement and he can't ever be charged even if the evidence is regarded as pretty conclusive. Freezing Putin's assets abroad would make the Russian leader sit up and take notice but Britain can't do that on its own. It would require international support. However good Scotland Yard and Wiltshire police are over the next few weeks in investigating this crime, the would-be assassins have fled and their trail may be impossible to uncover. The World Cup will still go ahead and England will be there playing in Russian football stadiums. And by then President Putin will have been reelected for another six years. So unless Boris Johnson and Amber Rudd have a secret scheme up their sleeve, Britain's response to the nerve agent attack will make little real difference.