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.

Countries join UK expelling Russian diplomats over spy poisoning Show all 24 1 /24 Countries join UK expelling Russian diplomats over spy poisoning Countries join UK expelling Russian diplomats over spy poisoning United States Donald Trump has expelled 60 Russian diplomats from the US and closed the consulate in response to the Sergei Skripal spy poisoning. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Great Britain Prime Minister Theresa May confirmed Britain would be expelling 23 Russian diplomats. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Ukraine Ukrainian president Petro Poroshenko has expelled 13 Russian diplomats. Getty Countries join UK expelling Russian diplomats over spy poisoning Germany Germany's Chancellor Angela Merkel has expelled 4 Russian diplomats. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning France France's President Emmanuel Macron has also expelled 4 Russian diplomats. Reuters Countries join UK expelling Russian diplomats over spy poisoning Poland Poland's President Andrzej Duda has expelled 4 Russian diplomats. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Lithuania President of Lithuania Dalia Grybauskaite has expelled 3 Russian diplomats. Getty Countries join UK expelling Russian diplomats over spy poisoning Czech Republic Czech Republic President Milos Zeman has also expelled 3 Russian diplomats. AFP Countries join UK expelling Russian diplomats over spy poisoning Netherlands Netherlands Prime minister Mark Rutte has expelled 2 Russian diplomats. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Latvia Prime Minister of Latvia Maris Kucinskis has expelled 1 Russian diplomat. Getty Countries join UK expelling Russian diplomats over spy poisoning Estonia Estonia's Prime Minister Juri Ratas has expelled 1 Russian diplomat. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Croatia Croatia President Kolinda Grabar-Kitarovic has expelled 1 Russian diplomat. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Italy Italian President Sergio Mattarella has expelled 2 Russian diplomats. Getty Countries join UK expelling Russian diplomats over spy poisoning Canada Canadian Prime Minister Justin Trudeau has expelled 4 Russian diplomats. Getty Countries join UK expelling Russian diplomats over spy poisoning Finland Finland's President Sauli Niinisto has expelled 1 Russian diplomat. Reuters Countries join UK expelling Russian diplomats over spy poisoning Denmark Danish Prime Minister Lars Lokke Rasmussen has expelled 2 Russian diplomats. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Romania Romania's President Klaus Werner Iohannis has expelled 1 Russian diplomat. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Norway Norwegian Prime Minister Erna Solberg has expelled 1 Russian diplomat. REUTERS Countries join UK expelling Russian diplomats over spy poisoning Spain Spanish Prime Minister Mariano Rajoy has expelled 2 Russian diplomats. Getty Countries join UK expelling Russian diplomats over spy poisoning Sweden Sweden's Prime Minister Stefan Lofven has expelled 1 Russian diplomat. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Albania Albanian President Ilir Meta has expelled 2 Russian diplomats. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Australia Australian Prime Minister Malcolm Turnbull has expelled 2 Russian diplomats. Getty Countries join UK expelling Russian diplomats over spy poisoning Macedonia Macedonia President Gjorge Ivanov has expelled 1 Russian diplomat. AFP/Getty Countries join UK expelling Russian diplomats over spy poisoning Hungary President of Hungary Janos Ader has expelled 1 Russian diplomat. AFP/Getty

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.