The Kremlin has “categorically denied” any involvement in the poisoning of two British citizens in Amesbury – the second reported case of poisoning by Soviet nerve agent novichok.

Speaking on Thursday in a press conference with journalists, presidential spokesman Dmitry Peskov said Britain had yet to produce any convincing evidence of either incident.

“At the very start, Russia offered a joint investigation,” he said. “The British side has shown no interest in our proposal.”

Other Russian institutions issued a more ridiculing response to the official British confirmation of the substance used, which was made late on Wednesday night.

“How dumb they think :ru: is to use “again” so-called “Novichok” in the middle of the FIFA World Cup… The show must go on?” wrote the official Twitter account of the Russian Embassy in the Netherlands.

As customary in breaking news events, state media initially limited reporting to the facts reported in foreign media. Later in the day, loyal speakers were wheeled out.

Sergei Zheleznyak, a member of the international relations committee of the lower house, said the British statements would be “met with laughter” among specialists: “Britain has to keep turning up the temperature of hysteria - and it does so because it is difficult for non-specialists to understand.”

Mr Zhelezhnyak said English football fans were helping to dispel the “worst of British propaganda directed against Russia.”

The possibilities brought up by a second Novichok poisoning has presented a challenge to the official British narrative. Either it means that British attempts to control further contamination were seriously flawed (and the UK response and investigation was less thorough than first presented.) Or there had been a secondary attack on a non-obvious target.

In uncredited comments to The Guardian, a “British minister” suggested the man and woman, both in their 40s, might have been specifically targeted by Russians to panic the civilian population. But in statements this morning, authorities suggested accidental poisoning was the most likely explanation, and was being given priority in the investigation.

Vladimir Uglev, one of the men credited with inventing the “Novichok” series of nerve agents, told The Independent that he was unsurprised that the substance had hung around.

“Unlike some of my colleagues, I’ve always said that it is very stable,” he said. “It can persist for years, with nothing much happening to it. There is a very, very, slow process of evaporation.”

According to the now-retired scientist, “Novichok” can bury itself in paint, trees, and, perhaps, in wooden benches: “It can get in and remain there for a very long time. If it is on a neutral surface, it will only degrade on account of evaporation. And that would be a long process.”

Mr Uglev suggested that the new outbreak might be connected with the behaviour of assassins. They were unlikely to have been issued with one batch of poison, he reasoned.