“For the best part of 18 months in the UK we have a homegrown, white supremacist, neo-Nazi terrorist organisation that is pursuing all the ambitions of any other terrorist organisation committed to violence,” Rowley said.

“That should be a matter of great concern for all of us.”

Since the first of the 2017 deadly attacks last March, Rowley said police had foiled 10 Islamist conspiracies and four far-right plots, although he said he could not provide details of these as they were subject to ongoing court cases.

To show the overall scale of the threat Britain faced, he said there were 600 terrorism investigations currently ongoing involving more than 3,000 suspects.

Over the last three years, terrorism arrests had doubled while in the same period some 2,000 people have been referred to the government’s counter-radicalisation Prevent programme, with a third of these over far-right concerns, he said.

Rowley, who next month steps down from the role he took on in 2014, said Islamist and far-right extremists were a toxic combination, feeding off each other and pursuing the same agenda of division, fear and hatred.

He reiterated British concern about extremists’ use of the internet and said he expected technology and internet firms would react to a mixture of persuasion and regulation as the
banking sector had done.

He also said it was important that an agreement struck with the European Union for when Britain leaves the bloc in 2019 did not damage relations with their European colleagues.

“Whatever the arrangements, we need something that provides at least a good a platform for cooperation as we have today,” he said.