Theresa May condemned Vladimir Putin’s “irresponsible” actions in a frosty meeting between the two leaders dominated by exchanges about the Salisbury nerve agent attack.

The Prime Minister was stony-faced as she shook hands with the Russian president before talks in which she told him the use of the Novichok nerve agent in the Wiltshire city was a “truly despicable act”.

She said the UK had “irrefutable” evidence that Russia was behind the attack on former spy Sergei Skripal and his daughter Yulia in March 2018.

It comes after she told ITV News ahead of the meeting that she would use the occasion to urge Mr Putin to hand over the two suspects in the case, adding: "We will be making every effort to bring them to justice."

Both Sergei and Yulia survived the poisoning in Salisbury, but in July 2018 Dawn Sturgess died after coming into contact with Novichok which is believed to have been in a perfume bottle.

Mrs May held her first formal meeting with Mr Putin since the Novichok attack in the margins of the G20 summit in Osaka.

“She told the president that there cannot be a normalisation of our bilateral relationship until Russia stops the irresponsible and destabilising activity that threatens the UK and its allies – including hostile interventions in other countries, disinformation and cyber attacks – which undermine Russia’s standing in the world,” a Downing Street spokesman said.

“The Prime Minister said that the use of a deadly nerve agent on the streets of Salisbury formed part of a wider pattern of unacceptable behaviour and was a truly despicable act that led to the death of a British citizen, Dawn Sturgess.”

The spokeman's words echoed what the Prime Minister told ITV News earlier in the day, as she insisted she would be making her position "clear".

The UK believes Moscow’s GRU military intelligence agency was behind the attack.

Scotland Yard and the Crown Prosecution Service believe there is sufficient evidence to charge two Russians – known by the aliases Alexander Petrov and Ruslan Boshirov – with offences including conspiracy to murder over the attack on the Skripals.

Online investigation group Belingcat said Boshirov is actually the highly decorated Colonel Anatoliy Chepiga, and Petrov is a military doctor called Alexander Mishkin.

Downing Street said Mrs May was “clear that the UK has irrefutable evidence that Russia was behind the attack – based on painstaking investigations and co-operation with our allies.

“She said that this behaviour could never be repeated and that the UK wants to see the two individuals responsible brought to justice.”

Alexander Petrov, left, and Ruslan Boshirov Credit: Metropolitan Police/PA

The UK expelled 23 Russian diplomats Mrs May claimed were undeclared intelligence officers following the Salisbury attack and international allies including the US followed suit.

But the Russian president has dismissed the Salisbury incident as “fuss about spies and counter-spies” that was “not worth serious interstate relations” and said “traitors must be punished”.

In an interview with the Financial Times, Mr Putin said: “Listen, all this fuss about spies and counterspies, it is not worth serious interstate relations. This spy story, as we say, it is not worth five kopecks. Or even five pounds, for that matter.

“And the issues concerning interstate relations, they are measured in billions and the fate of millions of people. How can we compare one with the other?”

The talks were 'serious in tone', a spokesman said. Credit: PA

Mr Putin added: “Treason is the gravest crime possible and traitors must be punished. I am not saying that the Salisbury incident is the way to do it. Not at all. But traitors must be punished.”

He also said liberalism had “become obsolete” but Downing Street said Mrs May told him “the UK would continue to unequivocally defend liberal democracy and protect the human rights and equality of all groups, including LGBT people”.

Treason is the gravest crime possible and traitors must be punished. I am not saying that the Salisbury incident is the way to do it. Not at all. But traitors must be punished

Vladimir Putin

The Prime Minister used the meeting with Mr Putin to say the UK remained “open to a different relationship” with the Kremlin but for that to happen “the Russian government must choose a different path”.

She also used the meeting to raise Russia’s actions in Syria and Ukraine.

The talks lasted one hour and 20 minutes and were “serious in tone”, a senior British official said.

For the first 40 minutes, when Mrs May raised the Salisbury case, she was alone with the Russian president apart from their interpreters.

“It was very worthwhile to be able to deliver some very serious messages face to face,” the official said.

Ahead of her showdown with Mr Putin, the Prime Minister met Japanese counterpart Shinzo Abe, the summit’s host, for a distinctly warmer meeting.

Mrs May said: “The UK and Japan are natural partners and we will continue to work together to uphold the global rules by which we seek to ensure a peaceful and prosperous world.”

During her interview with ITV News, she also hinted at what the future held for her once she steps down later this month.

She indicated she would not be seeking a spot in her successor's Cabinet, saying: "I look forward to returning to the backbenches."