In this age of modern warfare, the U.K. might already be at war with Russia, according to the former head of Britain's domestic intelligence agency.

Baroness Eliza Manningham-Buller, who led MI5 from 2002 to 2007, told the Lord Speaker's Corner podcast that Russia's escalating hybrid warfare tactics indicate a sustained campaign of hostility against Britain and its allies, The Times U.K. reported Monday.

"Fiona Hill may be right in saying we're already at war with Russia," Manningham-Buller said, referencing the prominent foreign policy expert and Vladimir Putin biographer who was key in testifying against President Donald Trump in the first impeachment.

"It's a different sort of war, but the hostility, the cyberattacks, the physical attacks, [and] intelligence work is extensive."

Her remarks reflect growing concern in London over "hybrid warfare" — a blend of cyber operations, disinformation campaigns, sabotage, and targeted violence — that many intelligence officials believe Moscow is deploying against the U.K. and NATO nations.

"We all hoped that at the end of the Soviet Union we would have a potential partner," she said. "That was one of the reasons why Putin was with us for the G8 summit in 2005. I met him when he came back to London.

"But actually we were wrong, because Russia is extremely hostile to the West. I didn't anticipate that within a year he'd be ordering the murder on London streets of Alexander Litvinenko."

Litvinenko, a former Russian intelligence officer, was poisoned with radioactive polonium-210 in London in 2006 — a killing a British inquiry concluded was carried out by Russian agents, likely on Putin's orders.

Russia's posture since its 2022 invasion of Ukraine has only intensified the threat, according to Manningham-Buller, because contending with sabotage, intelligence collection, attacking people are actions consistent with a state of ongoing conflict.

The Metropolitan Police's counterterrorism chief Dominic Murphy echoed those concerns over the weekend, warning hostile states are increasingly attempting to recruit or radicalize young people online.

"The online environment is the one that we're most concerned about," Murphy told the BBC's "Politics London." "In several of our cases we've seen young people, sometimes teenagers, being contacted online or proactively reaching out to organizations."

Hill, co-author of Labour Prime Minister Keir Starmer's 2025 Strategic Defence Review, said earlier this year that Britain faces "the rock" of Russian aggression and "the hard place" of a more unpredictable United States.

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