Russia has expressed frustration that the British authorities have denied them access Sergei Skripal, the former double agent they are accused of trying to kill using a Soviet-developed nerve agent. 

Speaking at a press conference in London on Thursday, the Russian ambassador to the UK, Alexander Yakovenko, accused Britain of “violating” diplomatic protocol by not sharing information on Sergei Skripal, 66, and his daughter Yulia, 33.

Yakovenko said: ”The only response we received from the British authorities was a Note Verbale about the medical condition of Yulia Skripal. It did not go further than the official public statements, according to which she was reportedly critically ill, but in a stable condition.”

Yakovenko claimed that by denying consular access to access Russian citizens, Britain had violated the Vienna Convention on consular services. 

“We continue to insist that the access and full information on the condition of our compatriots, whom nobody has seen since 4 March, should be provided,” he said. 

The British government has said there is “no other conclusion” other than the Russian state was behind the attack in Salisbury earlier this month, when the Skripals were found unresponsive on a bench in the centre of the town. 

Yakovenko dismissed the accusations and said Prime Minister Theresa May had “provided no proof ” and the UK Government had “built its official position on pure assumptions”.

He also claimed that the embassy had only learned about the death of Russian citizen, Nikolay Glushkov, last week from media reports, and claimed the “British side is deliberately ignoring our requests” for information about the case. 

Yakovenko also condemned the foreign minister Boris Johnson’s comparison of Russia hosting the World Cup later this year to Hitler’s 1936 Olympics, saying: “Nobody has the right to insult the Russian people, who defeated the Nazis.”

The Russian Foreign Ministry had previously responded by branding the comments “utterly disgusting” and “unacceptable”.

When asked if Johnson still had the support of the Prime Minister following the controversial comments, a Downing Street spokesman said Theresa May had “full confidence” in him.

Fans travelling to the World Cup have b een urged to follow Foreign Office advice. A spokesman said: “We want to ensure that our citizens are safe wherever they are in the world, as the Foreign Secretary said yesterday it’s for the Russian authorities to ensure the safety of visitors and we will be working with them on that.” 

Culture Secretary Matt Hancock had suggested that the best response to Russia hosting the tournament would be for England to win it. Asked if May agreed, the Downing Street spokesman said: “I think the Prime Minister would, of course, want our team to win the World Cup.”

Speaking before the press conference, the Russian embassy said its consular services had been “seriously affected” by the diplomatic row with the British Government, and it would be limiting visitors as a result.

It said: “As a result of the irresponsible actions of the UK Government, which led to an expulsion of 23 diplomats of the Russian embassy, including a number of Consular Section staff, the consular service for applicants has been seriously affected.

“This leaves us no option but to temporarily limit the number of all visitors. The embassy is doing its best to reestablish the ordinary workflow for the best functioning of the Consular Section, especially when it comes to providing assistance to Russian citizens and compatriots.”

The processing times for visa applications will be increased, the ambassador said.