Far-right terrorists pose an “organised and significant” threat to the UK, the county’s most senior terror officer has warned while revealing that four plots have been foiled in the past year.

Mark Rowley, assistant commissioner of the Metropolitan Police, made the figure public for the first time to “illustrate the growth of right-wing terrorism”.

“The right-wing terrorist threat is more significant and more challenging than perhaps the public debate gives it credit for,” he said.

“Right-wing terrorism wasn’t previously organised here.”

But security services have been warning of a shift since the murder of Labour MP Jo Cox in 2016, with the past year seeing five mainly Isis-inspired terror attacks leave 36 victims dead in London and Manchester.

Giving a lecture at an event held by the Policy Exchange think tank, Mr Rowley said: ”A deeply concerning characteristic is how both far-right and also Islamist terrorism are growing, allowing each side to reaffirm their grievances and justify their actions.“

He said police and MI5 have disrupted 10 Islamist plots and four far-right plots since the Westminster attack in March last year.

Mr Rowley, who is to retire next month, declined to give details of the four cases for legal reasons, but said they represent a combination of “organised and individual” action.

Family of Finsbury Park victim Makram Ali address media after Darren Osborne sentencing

He was speaking after a neo-Nazi was convicted of planning a terror attack at a gay pride event in Cumbria.

Ethan Stables, 20, wrote online that he was “going to war” after arming himself with weapons including a machete and axe and was arrested while walking to his target.

Another suspected far-right extremist is awaiting trial for allegedly planning to murder the Labour MP Rosie Cooper.

He and five other men arrested in connection with the plot are accused of being members of the neo-Nazi terrorist group National Action.

Several alleged members have been charged with terror offences, including serving British soldiers, following a wave of police operations.

It became the first far-right organisation to be banned by the Government in December 2016, sparking efforts by members to evade arrest by splitting into renamed regional factions including Scottish Dawn and NS131.

National Action gained notoriety for celebrating Thomas Mair, the far-right extremist who murdered Ms Cox during the EU referendum campaign.

Another fanatic, Darren Osborne, killed a grandfather when he rammed a hired van into Muslim worshippers leaving mosques in Finsbury Park in June.

The father-of-four, who was radicalised within weeks as he read far-right material by the former EDL leader Tommy Robinson, Britain First and others, was jailed for life last month.

Ethan Stables plotted to carry out a knife attack at a gay pride event (Greater Manchester Police)

Weyman Bennett, the joint secretary of United Against Fascism (UAF), said the group presented a “hidden danger”.

“Far-right terrorism is underestimated and is a threat to our democracy,” he told The Independent.

“There must be a renewed commitment to stopping the scapegoating of minorities that encourages it.”

Research and campaign group Hope Not Hate said that according to its count, 27 people were arrested or convicted of far-right inspired offences during 2017.

“Far-right terrorism and violent extremism is on the rise, something that concerns us greatly and which we have long warned the authorities to take note of,” said chief executive Nick Lowles.

“More worryingly, it is a trend which we fear is going to continue.

“The threat from the British far right is growing and evolving. Many see themselves in a war with Islam and as a result we must be prepared for more terrorist plots and use of extreme violence from the far right for the foreseeable future.”

A record number of people are being arrested on suspicion of terror offences in the UK, with the majority suspected of Islamist extremists but a growing proportion on the far right.

The trend was echoed in the first-ever figures provided by the Government’s controversial Prevent counter-terror initiative.

It shows that, of the total 7,631 people referred to Prevent in 2015-16, 65 per cent (4,997) were suspected of Islamist extremism and 10 per cent (759) of right-wing extremism.

Officials said Sikh and Northern Ireland-related radicalism was also seen, while a significant proportion could not be put into one category because of a more general “propensity towards mass murder and violence” that covers several groups.

Around a third of all those flagged were deemed to need no further action, half were passed on to alternative services and 14 per cent were considered by the counter-radicalisation Channel programme – where right-wing extremists make up more than a quarter of referees.

The Government’s revamped counter-terror strategy, which will be announced later this year, is expected to take a closer look at the far-right and ways to combat online messaging.

Finsbury Park attack Show all 14 1 /14 Finsbury Park attack Finsbury Park attack Police officers attend to the scene after a vehicle collided with pedestrians in the Finsbury Park, killing one person and injuring eight Reuters Finsbury Park attack The incident is being treated as a potential terror attack Reuters Finsbury Park attack A man has been arrested on suspicion of attempted murder Reuters Finsbury Park attack Police cordon off a street in Finsbury Park AFP/Getty Images Finsbury Park attack A man prays in the street after the attack Reuters Finsbury Park attack Men gather and pray together in the street in the aftermath of the attack AFP/Getty Finsbury Park attack Reuters Finsbury Park attack PA Finsbury Park attack Onlookers gather near a police cordon EPA Finsbury Park attack Forensic investigators arrive at the scene PA Finsbury Park attack A forensic tent stands next to a van PA Finsbury Park attack A police officer talks with residents AFP/Getty Images Finsbury Park attack Onlookers watch proceedings at the security cordon AFP/Getty Finsbury Park attack Local residents react at the scene AFP/Getty Images

While global efforts to remove terrorist propaganda has been largely focused on Isis, material like that consumed by Osborne as he prepared for the Finsbury Park terror attack is not illegal and remains online.

“You can’t police the internet,” a Channel intervention provider previously told The Independent. “As a society we need to understand where the risks are and investigate those who are vulnerable so they can be resilient.”

Security services have warned of the growing risk of “remote radicalisation” online, which has driven the mounting terror threat and become a hallmark of Isis’s bloody strategy to incite attacks worldwide.

Mr Rowley, who entered policing during the IRA attacks of the 1980s, took on his role as the national lead for UK counter-terrorism policing the day before Abu Bakr al-Baghdadi declared the so-called Islamic State.

He said Isis and other groups had become “more of a cult than an organisation”, shifting from regionally defined organisations to global movements.

Mr Rowley argued that the terror threat will be tackled only when the whole of society responds to extremism at its source, including local policing, education, councils, media, internet firms, communities and the Government.

With 600 ongoing investigations encompassing Islamist, extreme right-wing and other motivations, with more than 3,000 subjects of interest and more than 20,000 others who featured in past terrorism investigations, the challenge is unprecedented.

“I see extremists from Islamist and far-right persuasions both executing a common strategy” by exploiting existing grievances in target communities, generating distrust of state institutions and then “offering warped parallel alternatives”, Mr Rowley warned.