- Previous number of suspects have risen from 20,000 to 43,000
- Former counter-terror chief says new total is 'nine-tenths Islamic extremists'
- Separate Home Office figures show far-right make up less than a fifth in custody
- Current top terror police officer says right-wing is still fastest growing threat
- Numbers emerged after it was revealed Reading terror attack suspect was on list
A terror suspect watchlist has doubled in size from last year – but expert estimates and new figures suggest far-right extremists are just a tiny part of the problem.
Britain's top anti-terror officer Neil Basu has repeatedly said that right-wing extremism poses the fastest growing terror threat to the UK.
But while MI5's watchlist has doubled to 43,000 this year, experts say nine-tenths of these are jihadis.
New separate statistics from the Home Office on terrorists in custody, also show that of 238 people held for terrorism in Great Britain, 183 were Islamist extremists while just 44 were far-right. It is an increase of just 11 people from the same period last year.
They include a 17-year-old schoolboy jailed in January after a manifesto listing 'Areas to Attack' was found in his room.
The numbers came a day after senior military and intelligence expert Colonel Richard Kemp told the MailOnline he believed the focus on far-right terror was a 'false emphasis'.
Both sets of figures emerged in the aftermath of the Reading terror attack, which killed three people and saw another trio seriously hurt.
Richard Walton, former head of the Metropolitan Police Counter Terrorism Command, told the Telegraph the watchlist number was too big.
He said: "It is a ridiculously high number.
'The bigger question is why are there 40,000 people who think it is acceptable to consider murdering people. It tells you the scale of the problem.
'Nine-tenths of the people on that list are Islamist extremists.'
Home Secretary Priti Patel yesterday promised new laws to remove foreign criminals from Britain, declaring anyone who "abuses our hospitality" would be deported.
She said she would accelerate legislation on foreign offenders by making it easier to remove them, following the terror attack in Reading.
Funding for counter-terrorism policing is also set to increase to £906 million for next year - a rise of £90 million.
The two different sets of figures relating to counter-terrorism have emerged over the past few days.
Home Office figures show as of March 31 this year, there were 238 persons in custody for terrorism-related offences in Great Britain, an increase of 14 compared with the previous year.
A further 18% - 44 people - were categorised as holding far right-wing ideologies with the remaining prisoners (5%) holding beliefs related to other ideologies.
The government's watchlist document from March this year titled Transparency Report: Disruptive Powers 2018/2019, said MI5 was investigating approximately 3,000 subjects of interest (SOIs) across 600 priority investigations.
The document said as soon as MI5 judged an SOI no longer posed a threat, it was downgraded and placed in a "closed" category called Closed Subject of Interest (CSOI).
It went on to say the public figure for the number of CSOIs in 2017 was 20,000, and that there are now currently more than 40,000 CSOIs.
But it admitted although the cases were closed it was possible the subject of them could become dangerous again.
It added: 'This does not mean these SOIs will never pose a threat again, but merely that their current level of threat is not judged to be sufficient to prioritise allocating investigative resource against them.'
It continued to say the public figure for the number of CSOIs in 2017 was 20,000, and that there are now currently more than 40,000 CSOIs.
The report said: "A substantial element of the increase to over 40,000 is the inclusion of individuals who have never travelled to the UK but whose details have been passed to MI5 by foreign intelligence services, in order that MI5 be alerted should they enter t he UK.
"This new figure is not, therefore, directly comparable to the previous 20,000 figure and it does not mean there are now over twice as many CSOIs at risk of re-engagement."
"Nevertheless, by its very nature, the CSOI figure will always increase year on year.
"MI5 is constantly opening new investigations into individuals who come to its attention.'