THE attempted assassination of Sergei Skripal has left Ruth Davidson under pressure to cancel lunch with the wife of a Russian oligarch who made billions as Putin’s deputy finance minister.

Lubov Chernukhin, a Russian donor who has given the Tories £253,950 in the year to September 2017, bid £20,000 to have lunch with the MSP, at an auction at the UK party’s Black and White fundraising ball in February.

Yesterday, the widow of murdered dissident Alexander Litvinenko called on the party to return money linked to Putin’s brutal regime, saying the Tories needed to “be very careful who you are friends with”.

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The Tories have accepted £826,100 in Russian money since Theresa May became Prime Minister, according to the Sunday Times - despite her promise to distance the party billionaires who made their fortunes thanks to corruption in Moscow.

Litvinenko, whose husband was killed by the Kremlin in London in 2006, said: “These donations are not just from the heart and for charitable reasons. They are all calculated.”

She said the Conservative Party should put Britain’s national security interests “first”.

Chernukhin’s husband, Vladimir, was Putin’s deputy finance minister and then chairman of a state-controlled bank.

An SNP source said the Scottish Tory leader should “think long and hard about accepting a political donation from Putin’s pals, and that if she has any sense she would hand back the cash.”

The Tories have received more than £3m from Russian-linked tycoons and their companies, as well as from lobbyists for Moscow since their return to government in 2010.

Philip Hammond insisted there were “very strict rules” surrounding donations, which could only come from British citizens and were “carefully vetted”.

“There are people in this country who are British citizens who are of Russian origin. I don’t think we should taint them, or should tar them with Putin’s brush,” he said, saying the party would not be returning the cash.

A Sunday newspaper also reported that Andrey Pavlov, a Russian lawyer accused of a massive fraud, hired consulting firm, GPW, to prevent EU sanctions from being imposed on him.

In the engagement letter for the job, GPW promises to “draw on the experience” of its chairman, Andrew Fulton, a former MI6 officer and ex-chairman of the Scottish Tories. Fulton said last night he had “no recollection” of working for Pavlov.

There was pressure too on Alex Salmond over his weekly show on RT, the UK arm of the Kremlin backed broadcaster.

Yesterday, Shadow Chancellor John McDonnell, who has often appeared on the station, said he no longer would, accusing the broadcaster’s journalists of failing to be objective.

Earlier this week, RT suggested the Skripal and his daughter, who remain in critical condition had overdosed on recreational drugs.

McDonnell’s deputy, Peter Dowd, had appeared on the channel on Saturday, but the shadow chancellor said he would now recommend to colleagues “to step back”.

Tom Tugendhat, chairman of the Commons foreign affairs committee, last week called on Ofcom to review RT’s licence, accusing it of being a “hostile agent”.