The death of Portland businessman Stephen Curtis may be reviewed in a probe into up to 14 deaths linked to Russia following the poisoning of a double agent.

Mr Curtis, who had extensive business dealings with Russian oligarchs, died when the Augusta 109 helicopter he was travelling in crashed and exploded in a fireball in a field on approach to Bournemouth International Airport on March 3, 2004.

His pilot, Max Radford, also died in the crash.

The prospect was raised in Parliament yesterday by Labour's Yvette Cooper.

The comments came as Boris Johnson pledged to speak with Home Secretary Amber Rudd after calls for a fresh police investigation into 14 deaths in the UK that have been linked to Russia.

It emerged tonight that Russian double agent Sergei Skripal and his daughter, who were found slumped on a bench in Salisbury on Sunday, were poisoned with a nerve agent, counter-terror police believe.

Assistant Commissioner Mark Rowley, the head of counter-terrorism policing, said the incident was being treated as attempted murder and the pair had been "targeted specifically".

He declined to specify the nerve agent or how it was administered.

Former cabinet minister John Whittingdale, the former culture secretary, told MPs: "It is almost exactly four years since the annexation of the sovereign territory of Ukraine in Crimea by Russia.

"It is two years since the public inquiry concluded that President Putin almost certainly approved the murder of Alexander Litvinenko.

"Is it not clear, therefore, that existing sanctions are failing to deter Russia, possibly even from carrying out further assassinations on British soil.

"And that the time has come to impose far tougher sanctions against targeted individuals associated with President Putin's regime."

Foreign Secretary Mr Johnson said: "If the suspicions of members on all sides of this House are indeed confirmed, then that is going to have to be one of the options that we look at."

During the urgent question in the Commons Labour's Yvette Cooper also raised reports by BuzzFeed that 14 deaths in Britain had been linked to Russia by US spy agencies.

"What about the other 14 cases that several members have now raised of suspicious deaths, where UK authorities in many of these cases have concluded that these were suicides, despite the fact that there has now been considerable reported evidence, including in the BuzzFeed report, of further evidence that casts serious doubt on those conclusions," said Ms Cooper, chairwoman of the Home Affairs select committee.

"And also the claims that the US intelligence may have provided further evidence to the contrary in these individual 14 cases, and there are serious questions about whether the police investigations were thorough enough.

"Will he now, as a result of what he's said, discuss urgently with the Home Secretary whether an NCA investigation or other form of police further investigation and review of all of those 14 cases should now take place?"

It is believed that Mr Curtis's death is among the deaths being referred to.

Mr Johnson said: "There are a number of deeply troubling cases, (Alexander) Perepilichnyy, for instance, and to the best of our knowledge at present there is no further evidence that points in the direction of criminality.

"But I think what she says is very important and we will certainly follow it up and I will certainly have that discussion with the Home Secretary."

Mr Johnson later warned Russia is "certainly prepared to attack" UK infrastructure, amid concerns over moves to a reliance on electronic cards rather than cash.

Conservative former minister James Duddridge raised concerns, asking: "Is the Foreign Secretary particularly concerned about financial services infrastructure as we carry less cash and cheque books, we are reliant on our electronic cards."

Mr Johnson replied: "Absolutely. It's clear from the NotPetya attack and others that Russia is certainly prepared to attack our infrastructure and we should guard against that possibility with every preparation we can."

Conservative former minister Sir Edward Leigh said: "The way to preserve peace with Russia is peace through strength. There's no point giving commitments to the Baltics without hardware and men on the ground."

Elsewhere, Tory former attorney general Dominic Grieve, chairman of the Intelligence and Security committee which scrutinises the security services, said his committee's planned inquiry into Russian activities should get underway as a matter of urgency.

Committee member Keith Simpson asked Mr Johnson: "Would he agree with me that you can see the direction of travel over a decade now of the Putin regime?

"That the ability of them to murder people that they regard as traitors is in the finest traditions of the KGB, NKVD etc.

"And can he actually tell the House the measures that the British Government have taken, are they having any effect whatsoever on Putin?"

Mr Johnson said British sanctions have had an effect and the Russian economy "took a serious hit" as a result of those sanctions.

A book published in 2009 claimed that Portland-based lawyer Stephen Curtis may have been murdered.

Mr Curtis, who owned Pennsylvania Castle on Portland, made a name for himself running his own law firm in London, specialising in commercial and property transactions.

But it was his introduction to the Russian tycoon Mikhail Khodorkovsky which catapulted him into the world of billionaire businessmen, private jets, super-yachts and the inevitable intrigue that accompanied the lifestyle and dealings of the super-rich.

It also, allegedly, put him on a collision course with the Kremlin and would eventually cost him his life.

Curtis’s connections with the often-murky world of Russian business dealings deepened when he was introduced to another oligarch, Boris Berezovsky.

Berezovsky fell out spectacularly with the Russian authorities and became exiled in Britain.

He had long headed the list of Russia’s ‘most wanted’.

Berezovsky was closely associated with Alexander Litvinenko who was poisoned by radioactive material in London.

Khodorkovsky, who was among a handful of so-called oligarchs who made billions through the privatisation of state-controlled utilities, owned the Russian oil company Yukos.

He hired Curtis to manage the massive flow of money being generated by Yukos through Bank Menatap which had been set up by Khodorkovsky. It is alleged that the lawyer set up a complex financial network that stretched across the world and that Yukos money was channelled through offshore accounts in Gibraltar, the Cayman Islands and the Isle of Man.

As chief executive of Menatap, Curtis was at the centre of a power struggle between the then Russian president Vladimir Putin and Khodorkovsky.

Mr Curtis took the reins of the company when Mr Khodorkovsky was jailed for tax fraud, a charge his supporters believe was trumped up by the Russian authorities for political reasons.

It is then that things began to unravel for Stephen Curtis.

Following Khodorkovsky’s arrest at gunpoint in Siberia the lawyer allegedly told colleagues: “I cannot go back to Russia now. I will be arrested immediately.”

Shortly afterwards Menatap’s chairman Platon Lebedev was arrested on suspicion of fraud.

The Russian authorities were turning the screw on Yukos and many believed Putin had staked his reputation on bringing down some of the oligarchs who dared to question his authority.

It was later claimed that Mr Curtis was at the heart of a smear campaign against top Russian targets including President Putin and Chelsea supremo Roman Abramovich.

Mr Curtis was the chairman of the security firm ISC Global (UK) which worked for a group of Russian tycoons plotting against Putin.

ISC is alleged to have launched a campaign to discredit Mr Putin and 11 senior Russians, including Chelsea Football Club owner Mr Abramovich.

It is around this time, friends and colleagues claim, that Stephen Curtis began to fear for his life, according to the book Londongrad: From Russia With Cash.

The authors, Mark Hollingworth and Stewart Lansley, also claim that he was under constant surveillance in the weeks leading up to his death by private investigators acting for disgruntled shareholders in Yukos and by Russian state investigators. He reportedly moved his desk away from the window of his London office amid fears he could be targeted by a gunman.