MI5 believes Russian spies could be “active at all levels of British society”.

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Intelligence believes Vladimir Putin has ordered all sleeper agents working in secrecy in Britain to be operational. Spy hunters are already on the alert for possible cyber attacks

After the Ukraine war, up to 50 Russian spies could now be on the hunt in Britain.

MI5 believes Vladimir Putin has ordered all sleeper agents – under deep cover – to be ready to spring into action.

Spy hunters are already on the alert for possible cyberattacks in response to Britain’s support for Ukraine.

And intelligence chiefs fear agents will also try to steal our military secrets and target Russian dissidents and Ukrainian activists who live here.

Sources claim Putin has spies in every sector of British society, from top public schools to civil servants and the House of Commons.

A senior intelligence insider said: “We have to assume that Russia is now active at all levels of British society. They scoop up all sorts of information and return it to the Kremlin through handlers.

“This could be anything from the types of weapons being sent to Ukraine — and how much of them — to the sexual antics of the country’s political and military leaders.”

The revelation comes after a suspected Russian spy was arrested in Gatwick last week.

The man, in his 40s, was held under the Official Secrets Act and remains in custody.

Lt. Col. Philip Ingram, a former military intelligence officer, said: “It is impossible to estimate exactly how many Russian agents there are in the UK.

“Of course, there are different types – professed intelligence officers, known to be part of Russian diplomatic missions, and those operating covertly, trying to recruit agents and then sleeper agents in all sectors of society.

“Given our support for Ukraine, Russian intelligence will be heavily focused on operations inside the UK and could also include recruiting agents in political, defense and industrial bodies.”

It emerged last week that up to four Russian spies may have infiltrated the House of Commons. MP Chris Bryant said there had been no recent warnings to MPs about the presence of Russian agents.

But he said it was likely there were a “handful” of Russian moles in parliament.

“If the war is prolonged, I think Russia will go back to old Cold War-style espionage techniques,” Bryant said.

An Interior Ministry spokesman said: “We have made great strides in recent years to counter the threat posed by the Russian state and to increase our and our allies’ resilience to malicious Russian activities.”