Whether we can prove Moscow’s involvement in the Skripal case or not is irrelevant

Unhelpful as it undoubtedly is, the chief executive of Porton Down was well within his rights to state that his establishment is unable to determine the origin of the nerve agent that was used in the attack on the Skripals. Gary Aitkenhead’s intervention prompted the deletion of a Foreign Office tweet and has caused much embarrassment to Boris Johnson personally, the foreign secretary being the most gung-ho in blaming the Russians.

On his visit to Turkey, Vladimir Putin was almost gleeful in making capital out of the latest twist in the story. Despite everything, the Russians are sustaining their propaganda war against Britain, concocting ever more reasonable-sounding but insincere offers of help with the investigation, including calling an emergency session of the Organisation for the Prohibition of Chemical Weapons.

None of that alters the overwhelming probability that the novichok nerve agent originated in Russia and that, as the prime minister stated last month, the Russian authorities were either directly or indirectly responsible for this episode. The nerve agent, according to Porton Down, is weapons-grade and of a type that could only be used by a state agency.

It was Russia, during the Soviet era, that developed the novichok family of agents, and it was a Russian former spy who was the intended victim. It is inconceivable that anyone other than the Russians would have the ability and the motive to organise such an elaborate plot. We also have the precedent of the murder of Alexander Litvinenko to add to the body of evidence pointing to Russia.

The Russians response to all of this is to say “prove it”, as if in a court of law. Even on a legal test such as being beyond reasonable doubt or on the balance of probabilities, the Russians are plainly culpable. Yet a legal standard of proof is not required for countries to make a judgement and to take appropriate action, as so many of Britain’s friends and allies around the world have done.

Again, the Russians are playing a clever game by insisting, disingenuously, on a proof that is impossible to achieve. Some, such as Jeremy Corbyn, at various stages of this affair, seem to have bought that line, their suspicions of the Western intelligence agencies getting the better of their common sense. Yet whatever “dodgy dossiers” may have been generated in the past, the facts of the Salisbury case are not in doubt.

The Russians are on better ground when they claim that relations with the West are sliding into a new Cold War. That, of course, is in nobody’s interests, but it seems inevitable when Russia engages in such activities and threats and invades its neighbours.

The Skripal affair is a cause, consequence and a symbol of the complete breakdown in relations between Russia and the West. Since the collapse of the Soviet Union and the Eastern bloc a quarter of a century ago, Russia has lost an empire and has failed to find a new role. Under Vladimir Putin, the country seems intent on reprising its old role and returning to type. It is difficult to see how any new detente can be achieved in such circumstances as these.