Salisbury duo interviewed as a punishment, officials believe

it’s not at all plausible, it’s implausible deniability. That’s pretty much down to working across Government: police, intelligence agencies working with us both on the case and also how we’ve communicated that.”

The source added: “Right at the start of Salisbury there was a huge campaign of pro-Russia accounts pushing out the Russian narrative. We haven’t seen this since [the men were named].

“The social media networks have cracked down – Twitter has kicked off thousands of Russia-friendly or suspicious accounts that have created bots. It could [also] be a decision by the guys pushing the propaganda button in Moscow that acknowledge this isn’t the strongest story. It’s not really plausible so we’re not going to push it in the same way as we did in the start, when there was a more receptive audience.”

Theresa May told the House of Commons earlier this month that Petrov and Boshirov are officers of Vladimir Putin’s military spy agency.

Prosecutors said there is enough evidence to charge the men with offences including conspiracy to murder Mr Skripal and his daughter.

Mrs May told the Commons: “This was not a rogue operation. It was almost certainly also approved outside the GRU at a senior level of the Russian state.”

But the Crown Prosecution Service faces a battle to bring the case to court as Russia does not allow the extradition of its own nationals. A European arrest warrant for the two men has been obtained.

Following the attack, more than 150 Russian diplomats were expelled by nearly 30 countries across the world in a show of support for the UK.

Boshirov and Petrov made their much ridiculed TV appearance after Vladimir Putin, the Russian president, publicly called on them to speak to the media, leaving them with little choice but to take part in the stage-managed interview.

As expected, they denied being responsible, but their explanation of what they were doing in Salisbury prompted ridicule in several quarters.

They claimed friends had urged them to see the cathedral’s “famous 123m spire”, but that the snow and “muddy slush” meant their first trip to Salisbury was less than an hour because of train delays, forcing them to return the next day.

Boshirov and Petrov also denied taking a bottle of Nina Ricci perfume to carry the deadly Novichok poison with them to the UK.

“Isn’t it silly for decent lads to have women’s perfume? When you pass through customs they check all your things,” Boshirov said.

“That would raise questions even among ordinary people. Why does a man have women’s perfume? We didn’t have it,” Petrov said.

The men claim that being named by British police has left them too scared to go out.

Their account follows a barrage of Russian misinformation on social and mainstream media, with Whitehall sources saying that 40 different “counter narratives” have been used to undermine the British version of events.