LONDON - The head of counter terrorism policing in Britain revealed for the first time on Monday night that in the past 12 months police have thwarted four extreme right-wing terror plots.

London Metropolitan Assistant Commissioner Mark Rowley highlighted in a keynote speech how Islamist and right-wing extremists were both intent upon creating hatred, intolerance and division within British communities.

Ten well publicized terror plots by Islamists, including the attack last March on Westminster, had highlighted the danger to the public, but Rowley used a speech in London to warn about the dangers of extreme right wing plots.

He said: "It is important we make these figures public in order to illustrate the growth of right-wing terrorism. For the first time we have a home-grown proscribed white-supremacist neo-Nazi terror group, which seeks to plan attacks and build international networks."

"The right-wing terrorist threat is more significant and more challenging than perhaps the public debate gives it credit for. Right-wing terrorism wasn't previously organised here," he said.

Rowley declined to give details of the four cases he revealed for legal reasons, but added that they had represented a combination of "organised and individual" action.

Rowley was delivering the seventh Colin Cramphorn Memorial lecture entitled "Extremism and Terrorism: The need for a whole society response". His lecture came as he prepares to retire from policing after 31 years.

Speaking about his own reflections during his tenure, Rowley said the acute threat from terrorism could only be tackled when the whole of society responded to the chronic threat from extremism.

Describing 2017 as an extraordinary and most challenging of years, Rowley said it saw five terror attacks in Britain, four Islamist and one extreme right wing. A total of 36 people died and hundreds more were injured in the attacks.

Rowley paid tribute to colleagues in policing and the security services for their extraordinary efforts over the past four years in confronting the threat.