Russian President Vladimir Putin says it is nonsense to think that Moscow poisoned former Russian spy Sergei Skripal and his daughter, who are critically ill in a British hospital.

Britain has said that Mr Skripal and his daughter were poisoned by the Soviet-era ‘Novichok’ nerve agent, and British Foreign Secretary Boris Johnson said on Sunday that Russia has been stockpiling it and investigating how such weapons could be used in assassinations.

But Mr Putin, in his first detailed comments on the poisoning, said Russia had been falsely accused.

“As for the tragedy that you mentioned, I found out about it from the media. The first thing that entered my head was that if it had been a military-grade nerve agent, the people would have died on the spot,” Mr Putin told reporters.

“Secondly, Russia does not have such (nerve) agents,” he said.

“We destroyed all our chemical weapons under the supervision of international organisations, and we did it first, unlike some of our partners who promised to do it, but unfortunately did not keep their promises.” 

Sergei Skripal was convicted of spying for the UK. Photo: Getty

Despite the tensions, Mr Putin said Moscow was ready to co-operate with London.

“We are ready to co-operate, we said that straight away, we are ready to take part in the necessary investigations, but for that there needs be a desire from the other side, and we don’t see that yet. But we are not taking it off the agenda, joint efforts are possible,” he said.

As a whole, of course, I think any sensible person would understand that it would be rubbish, drivel, nonsense, for Russia to embark on such an escapade on the eve of a presidential election. It’s just unthinkable.”

Mr Putin was speaking after winning a new term in Russia’s presidential election.

British officials have said Moscow was culpable for the poisoning and expelled 23 Russian diplomats based in London.

Moscow retaliated on Saturday by expelling the same number of British diplomats from Moscow, shuttering the British consulate in Russia’s second city of St Petersburg and closing down the Russian activities of the British Council, which promoted British culture overseas.

Mr Johnson earlier said Britain had evidence of Russia’s development and stockpiling of nerve agents.

“We actually have evidence within the last 10 years that Russia has not only been investigating the delivery of nerve agents for the purposes of assassination, but has also been creating and stockpiling Novichok,” he told the BBC.

Mr Johnson said Russia’s reaction “was not the response of a country that really believes itself to be innocent”.

“Their response has been a mix of smug sarcasm and denial and obfuscation,” he said.

Mr Johnson said Britain’s National Security Council will meet later this week to decide “what further measures, if any” may be taken, and that the government may decide to target Russian wealth in Britain.

The British capital has been dubbed “Londongrad” over the large quantities of Russian money that have poured in since the collapse of the Soviet Union in 1991.

Some British MPs have urged Prime Minister Theresa May to freeze the private assets of senior members in Russian President Vladimir Putin’s circle.