Russia’s ability to spy in Europe has been dealt the “most significant strategic blow” in recent history after coordinated expulsions of diplomats since the invasion of Ukraine, with a hundred diplomatic visa requests refused in the UK alone in recent years, according to the head of the UK’s security services, MI5.

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Ken McCallum, the director general of MI5, said in an annual speech outlining threats to the United Kingdom that this year 600 Russians officials had been expelled from Europe, 400 of whom his agency judged to be spies.

“We’ve continued to work intensively to make the UK the hardest possible operating environment for Russian covert action,” said McCallum. “In the UK’s case, since our removal for 23 Russian spies posing as diplomats, we have refused on national security grounds over 100 diplomatic visa applications … the serious point is that the UK must be ready for Russian aggression for years to come.”

In comments after the speech, McCallum called the expulsions “a very, very large dent in the Russians call about positioning across Europe,” adding data about agents was shared between European allies so that “it’s not easy for the Russians to cross post” one spy “expelled from country A to Country D.”

He added: “I hope what will continue to be true is that a very large volume of trained, experienced Russian intelligence talent, if I can use that term, will be of far less utility and most other parts of the world for many years to come.”

The speech also revealed a growing threat of Iranian state foul play including “ambitions to kidnap or kill British or UK-based individuals perceived as enemies of the regime”, said McCallum. He revealed there have been 10 “such potential threats since January alone in the UK”.