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Boris Johnson today warned Vladimir Putin that he will be “proved wrong by history” after the Russian President suggested Western liberalism was “obsolete”.

Speaking to the Evening Standard, Mr Johnson, the frontrunner to be the next prime minister, also hit back against the Russian leader over the Salisbury Novichok poisonings, stressing the need for “justice, the rule of law and a simple code of decency in international relations”.

His strong words suggested that he would be prepared to be tough with Russia over aggressive acts if he gains the keys to No 10.

Mr Johnson spoke out after Mr Putin sparked a fierce debate among world leaders at the G20 summit in Japan over the values which have underpinned Western democracies for decades.

In an interview with The Financial Times, the Russian leader said “the liberal idea” had “outlived its purpose”.

However, Mr Johnson rejected this argument and also highlighted how the West had united against Moscow over the poisonings, in which former Russian double agent Sergei Skripal and his daughter Yulia came into contact with the military-grade nerve agent in March last year.

The attack was allegedly carried out by agents from Russian military intelligence. The Kremlin has denied Russia was involved.

The former foreign secretary said: “Vladimir Putin will be proved wrong by history — liberalism will continue to triumph.

“I saw first hand how nations across the world came together to back Britain and back the international order with 28 countries expelling 153 [Russian] diplomats.

"Together we stuck up for justice, the rule of law and a simple code of decency in international relations.”

Mr Putin appeared to want to move on from the row which damaged Anglo-Russian relations. “Listen, all this fuss about spies and counterspies, it is not worth serious interstate relations,” he said. “This spy story, as we say, it is not worth five kopecks.”

He 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 ... but traitors must be punished.”

Ahead of a meeting with Mr Putin, Theresa May stressed that the suspects in the Salisbury attack should be “brought to justice” and that “it can’t be business as usual with Russia until they stop the sort of acts we have seen them doing around the world”, including alleged cyberattacks and spreading of disinformation.

The Prime Minister treated Mr Putin with disdain as the pair shook hands before their meeting.

Mrs May held out her hand but quickly looked away from the Russian leader. Sources in the room said the talks were “frosty”. Britain believes at least two officers from Russia’s military intelligence service, the GRU, were behind the poisoning of Mr Skripal and his daughter. They both survived but Dawn Sturgess died last July after accidentally coming into contact with the Novichok by handling a contaminated perfume bottle.

Mr Putin also trumpeted the rise of populist movements in America and Europe, criticising as a “cardinal mistake” German Chancellor Angela Merkel’s decision to allow a million migrants, many from war-ravaged Syria, into her country.

“This liberal idea presupposes that nothing needs to be done. That migrants can kill, plunder and rape with impunity because their rights as migrants have to be protected.

“Every crime must have its punishment. The liberal idea has become obsolete. It has come into conflict with the interests of the overwhelming majority of the population.”

But his remarks were swiftly criticised by political figures in the West.

Foreign Secretary Jeremy Hunt, Mr Johnson’s rival in the Tory leadership race, tweeted: “This just shows what we’re up against. Corbyn at home, and people trying to subvert our values from abroad.

“Our democratic system based on rules, respect for individual rights & human dignity has created more happiness & wealth than any other way of life anywhere in the world.”

European Council president Donald Tusk tweeted: “What I find really obsolete is authoritarianism, personality cults and the rule of oligarchs.”

Elsewhere at the G20, Mr Putin staged talks with Chinese leader Xi Jinping and Indian Prime Minister Narendra Modi, where they discussed closer ties.

Mr Putin said they agreed on the need to respect national sovereignty and refrain from interference in other states.