Dozens of Russian oligarchs in Britain are set to have their assets seized in the wake of the Salisbury revelations.

A Whitehall source said the National Crime Agency could target 'more than 100' foreigners with 'unexplained wealth orders' in the coming months. The majority are understood to be Russian.

Police were given new powers at the start of this year to apply for the orders against foreigners in the UK suspected of having links to corruption or organised crime abroad.

The orders require suspects to prove to the courts how property and assets held in the UK were funded.

Dozens of Russian oligarchs in Britain are set to have their assets seized in the wake of the Salisbury revelations. The super-rich who could face crackdown includes Roman Ambramovich

If they cannot show the assets were legally obtained, then the authorities can apply for confiscation.

Critics of Vladimir Putin's regime have long called on the UK to act against the 'dirty money' said to be laundered in London by cronies of the Russian President.

In March, the Liberal Democrat leader Sir Vince Cable cited the case of Igor Shuvalov, former first deputy prime minister of Russia, who owns two flats in Whitehall near the Ministry of Defence bought in 2014 for £11.4 million.

An official declaration by Mr Shuvalov in 2014, while still in office, said his salary was £112,000.

In March, the Liberal Democrat leader Sir Vince Cable cited the case of Igor Shuvalov

Ministers faced criticism in the summer when it emerged that the new wealth orders had been used just three times in the first six months.

But Whitehall insiders said the NCA had dozens more cases in the pipeline, after Theresa May ordered a crackdown following the novichok attack in March. One said: 'There is a lot going on that the public can't see in terms of visas and investigations into individuals' wealth. The NCA is looking at more than 100 cases, but these things take time to get right. People might have noticed that Roman Abramovich isn't in the country any more.'

Security Minister Ben Wallace yesterday bridled at suggestions that the UK authorities had taken their eye off the ball, saying: 'Watch this space.'

In the Commons, Attorney General Geoffrey Cox told MPs that a 'considerable number' of unexplained wealth orders would be issued in the coming months. He called them 'a particularity valuable part of the armoury of the law enforcement agencies against corruption and bribery'.

Igor owns two flats in Whitehall near the Ministry of Defence bought in 2014 for £11.4 million

He added: 'They are a novel tool – we're currently looking, the Government is looking and the law enforcement agency is looking at correct and appropriate cases to use them.

'I'm not aware yet whether there's been any estimate of what might be realised by their use, but I expect to see that a considerable number of them will be used over the coming months.'

Downing Street said the UK was also taking more steps to stop anyone suspected of 'hostile state activity' at the border. Russian oligarchs linked to Mr Putin face a string of clampdowns in London, including searches of private flights.

Officials are already conducting a review of all 'tier one' visas, which allow foreign individuals to live in the UK if they are investing at least £2million.

Critics of Vladimir Putin's regime have long called on the UK to act against the 'dirty money' said to be laundered in London by cronies of the Russian President

New rules state that visas can be refused if there are 'reasonable grounds to believe ... the funds were obtained unlawfully or by conduct which would be unlawful in the UK, or if the character or conduct or associations of a third party providing the funds is not conducive to public good.'

Chelsea owner Roman Abramovich, a close friend of Mr Putin, did not have his visa renewed when it expired in May, without any reason given. He later withdrew his application.

Police say there 'is no basis on which to re-open' inquiries into up to 14 deaths potentially linked to Russian death squads.

Ex-home secretary Amber Rudd ordered the claims to be examined after the Salisbury attack. The deaths had been found to be the result of heart attacks, suicides, accidents or natural causes.