MI5 Director General Andrew Parker
MI5 Director General Andrew ParkerReuters

Britain and the European Union must build a close security partnership after Britain leaves the EU in order to foil Islamic State (ISIS) attacks, the head of Britain’s domestic spy agency says.

The comments by MI5 chief Andrew Parker will come in an event on Monday in Berlin hosted by Germany’s BfV domestic intelligence service. Excerpts of the speech were made available to the Reuters news agency on Sunday.

Parker is set to warn that Islamic State jihadists are plotting “devastating and more complex attacks.”

“European intelligence cooperation today is simply unrecognizable to what it looked like five years ago,” he will say, adding, “In today’s uncertain world, we need that shared strength more than ever.”

Parker has several times in recent years warned of an increased terror threat in Britain. Last July, he said British intelligence services are facing an "intense" challenge from terrorism, adding there was currently "more terrorist activity coming at us, more quickly" and that it can also be "harder to detect".

Two years before that, in 2015, he warned that ISIS terrorists were planning to launch a mass casualty terror attack in the UK.

Britain suffered four deadly attacks last year that killed 36 people.

In March, a man killed five people after driving a into pedestrians on Westminster Bridge in London before stabbing a policeman to death outside parliament.

ISIS claimed responsibility for that attack, saying the attacker was one of its “soldiers”, though British police later said they had found no evidence that the terrorist was indeed associated with ISIS.

The Westminster Bridge attack was followed by a suicide bombing at a pop concert in Manchester which killed 22. The following month eight people died after three Islamists drove into pedestrians on London Bridge and stabbed people at nearby restaurants and bars.

Two weeks later a van was driven into worshippers near a London mosque which left one man dead.

Speaking ahead of the May 22 anniversary of the Manchester bombing, Parker said that 12 plots had been thwarted since the Westminster attack, bringing the total number of disrupted attacks since 2013 to 25, according to Reuters.

He praised the Counter-Terrorism Group (CTG), which groups all 28 European Union countries, Switzerland and Norway, for its exchange of intelligence.