Deep-cover Russian spies are embedded in our society, security officials believe.
Up to a dozen highly trained “illegals” may have been here for years in one or two-person cells.
Now the Government is poised to ramp up MI5’s powers to tackle undeclared spies by making their presence in the UK illegal.
It follows the report into Kremlin interference in the Brexit referendum, which called for a crackdown on spy activity in the UK.
Included in a review of the Official Secrets Act will be a form of foreign intelligence officer registration, which spies will have to sign on entering the UK or risk being prosecuted and jailed.
It is not currently a crime to live here as an undercover officer.
The Government is also invoking the Magnitsky Act, named after murdered Moscow lawyer Sergei Magnitsky, which can allow the freezing of Russians’ assets.
Prime Minister Boris Johnson said: “This Government is bringing forward legislation, not only a new Espionage Act, not only new laws to protect against theft of our intellectual property but also a Magnitsky Act directly to counter individuals in Russia or elsewhere who transgress human rights.”
Sources say the undeclared “illegals” are trained in Soviet-style spy schools outside Moscow.
They could be used for pre-mission surveillance and one may even have helped prepare the novichok attack on Sergei Skripal.
Referring to the Russian spy service, a former military intelligence officer said: “It is remotely possible the GRU were helped in the Salisbury attack by an illegal.”
Other information undercover officers could provide might include data on coastal terrain or local troop movements.
Crucially they would also know what to look for in critical infrastructure such as dams, water systems and power networks or installations to be targeted for sabotage.
Russia’s most celebrated “illegal” was Anna Chapman, who remained undercover for many years in Britain and the US before being rumbled by the FBI in 2010.
Security Minister James Brokenshire said: “We are clear-eyed in relation to the threat that Russia poses, that is why we have taken the steps that we have taken.
“There can be no normalisation of our bilateral relationship until Russia ends the destabilising activity that threatens the UK and our allies and undermines the safety of our citizens.”
Labour ’s Nick Thomas-Symonds told the Commons that British security agencies need help tackling Russian spies.
He said: “They have not received the strategic support, the legislative tools or the resources necessary to defend our interests.”
Yesterday the PM again hit back at claims the Kremlin might have helped sway the Brexit vote, saying: “Let’s be in no doubt what this is really all about – this is about pressure from the Islingtonian Remainers who have seized on this report to try to give the impression that Russian interference was somehow responsible for Brexit.
“The people of this country didn’t vote to leave the EU because of… Russian interference, they voted because they wanted to take back control of our money, our trade policy and our laws.”