Theresa May believes that Russian and former Soviet bloc oligarchs with links to Vladimir Putin became too close to the Tories under David Cameron and should be barred from party fundraising events, The Mail on Sunday understands.

Amid mounting international tension over the alleged espionage activities of Putin's foreign agents, the Prime Minister objects to lavish party functions being dominated by billionaire Russians with opaque pasts who are able to rub shoulders with Cabinet Ministers.

Mrs May also disapproves of MPs taking part in Anglo-Russian parliamentary groups – or 'MP forums' – believing them a 'security risk'.

Theresa May believes that Russian and former Soviet bloc oligarchs with links to Vladimir Putin became too close to the Tories under David Cameron

Her stance signals a break with the Cameron era, when Moscow-linked businessmen contributed an estimated £1 million to Conservative funds through auctions, dinners and other donations.

In a symbolic move, the next fundraiser – the Black And White ball in February where tables with Cabinet Ministers go for £15,000 each – will for the first time be attended by a group of ordinary party members offered cut-price tickets.

One of the most notorious incidents came during a 2014 summer ball at the Hurlingham Club, when the wife of billionaire Vladimir Chernukhin, a former finance minister under Putin, paid £160,000 for a doubles tennis match with Boris Johnson and David Cameron. The game was later cancelled amid a furore and the money refused.

A senior political source said: 'During six years as Home Secretary, Theresa was made acutely aware by the intelligence services of the growing threat posed by Russian agents operating on British soil.

'She thinks it is sensible to sup with a long spoon when it comes to Moscow, and that wasn't always the case under the previous administration.'

The source added that Mrs May had said she would 'rather not' have oligarchs at the next Black and White party.

Alexander Temerko (left) chats with David Cameron (centre)

Her intervention comes as relations between Moscow and Washington were shaken last week by President Obama's decision to expel 35 Russian diplomats amid a row over US claims that the country directed cyber-attacks on the Democratic Party and Hillary Clinton's bid to win the White House, which helped Donald Trump's campaign.

Putin said that he would not 'stoop' to expelling American diplomats in a tit-for-tat retaliation, but would work to restore ties when Trump takes office on January 20.

There are now believed to be more Russian spies trying to gather intelligence in Britain than at the height of the Cold War, with weapons manufacturers, the Armed Forces and City institutions high on the list of their targets.

Last month, Andrew Parker, the head of MI5, made an unprecedented public statement about the threat, warning that Russia was at 'work across Europe and in the UK' and carrying out a 'high volume' of secret activity as it adopts an 'increasingly aggressive' approach to pursuing its foreign policy goals. The Kremlin described his claims as 'unfounded and baseless'.

Mrs May's reservations about 'MP forums' are a reference to groups such as the Conservative Friends of Russia, which was launched in August 2012 at the Russian Embassy in London with Tory MPs including John Whittingdale, Andrew Rosindell and Nigel Evans as vice-presidents.

It had been closed by the end of the year after being accused of an attempt to smear outspoken anti-Putin Labour MP Chris Bryant by posting an infamous picture of him posing in his underpants.

Tatiana Borodin and Andrey Borodi at a bash in 2014

Leaked emails showed that the organisation had been in contact with a diplomat at the Russian embassy who was connected to the intelligence services.

Other Russians who have taken a prominent role at Tory fund-raisers include Andrey Borodin, a financier wanted in Moscow over allegations (which he denies) of a £220 million fraud, who sat on the same table as Boris Johnson at the 2013 Black and White event.

And Ukrainian-born Leonard Blavatnik, worth £13 billion, was reported to have secured a 'prime spot' at the 2016 Black and White Ball, along with his former countryman, businessman Alexander Temerko, who donated £220,000 to 24 Tory MPs, and who sat next to Health Secretary Jeremy Hunt at a 2015 Carlton Club fundraiser.

A Downing Street spokesman declined to comment directly on the oligarch 'ban', but said that 100 party members would be offered tickets for the Black and White party at the discounted rate of £75. There would also be a number of complimentary tickets for 'the most hard-working campaigners and party supporters'.

Putin's cash is as corrosive as his hackers

By Mark Almond

The old year ended with screaming headlines about Russia hacking the US elections and President Obama's retaliation.

But if there's one thing more likely to corrupt democracy than hacking, it's money. That's why Theresa May is so worried about the endless flow of Russian cash into London, which she fears has the real potential to buy influence and poison public attitudes.

And it is such stealth tactics which are the hallmark of Putin's approach to the West.

Many were surprised that when Obama expelled Russian diplomats in response, Putin switched on a charm offensive and invited American children to a Christmas party in Moscow.

Putin plays a clever game to get what he wants, which is preventing US-sponsored regime change in the Middle East

He is not turning sentimental.

Standing up to America may be good for his popularity at home, but, already in his 60s, Putin is not going to gamble his lifetime's tenure in the Kremlin by forcing a showdown with the West.

So he plays a clever game to get what he wants – which is preventing US-sponsored regime change in the Middle East, or closer to home in countries such as Ukraine. He also wants sanctions imposed by the West on Russia lifted.

One tactic is to play America and China off against each other. The two are already on a collision course over influence and trade and Russia, the third major power, will try to extract concessions from either side in return for support. Russia is weaker than China or America, but weight is not always decisive, as the Kremlin's judo black belt knows.

Trump intends to be global No 1, but Putin can accept that provided he is left alone in his own sphere of influence. Letting Trump stand centre stage will leave the Kremlin free to get on with its agenda in the shadows. That could keep both men happy in 2017.

Meanwhile, Putin can hardly fail to be pleased at the remarkable spread of Russian influence in Britain as he seeks to loosen the ties that bind Nato together.

Mrs May is right to be vigilant – and right to urge our European allies to play their part and make a full financial contribution.