Britain is facing the severest terror threat since the height of the IRA bombings in the 1970s, the new terrorism watchdog has warned.

Max Hill, who has recently taken up the role, claims the UK faces a heightened risk of attacks from Isis, with the ideological group planning “indiscriminate attacks on innocent civilians”.

He likened the scale of bombing threats to that posed by the Irish Republican Army (IRA) four decades ago, when the group was highly active.

The terror group targeted, buses, pubs to even parliament, killing dozens of people.

Similar to the IRA, Mr Hill told The Telegraph Isis was targeting UK cities, and was reaching a critical point with “enormous ongoing risk which none of us can ignore.”

He said: “In terms of the threat that’s represented, I think the intensity and the potential frequency of serious plot planning – with a view to indiscriminate attacks on innocent civilians of whatever race or colour in metropolitan areas – represents an enormous on-going risk that none of us can ignore.

Terrorism in 2016: Terror attacks in Europe claimed by Isis Show all 9 1 /9 Terrorism in 2016: Terror attacks in Europe claimed by Isis Terrorism in 2016: Terror attacks in Europe claimed by Isis Policemen outside Rouen's cathedral during the funeral of Jacques Hamel, the priest who was killed in a church in Saint-Etienne-du-Rouvray in Normandy on 26 July during a hostage-taking claimed by Islamic State group Joel Saget/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis Two jihadists, both 19, slit Hamel's throat while he was celebrating mass in an attack that shocked France as well as the Catholic Church Joel Saget/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis Muslims place flowers and hold a minute of silence in front of the church if Saint-Etienne-du-Rouvray, western France, where French priest Jacques Hamel was killed on 26 July Charly Triballeau/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis Two people hold each other by the new makeshift memorial in Nice, in tribute to the victims of the deadly Bastille Day attack at the Promenade des Anglais Valery Hache/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis The Islamic State group claimed responsibility for the truck attack that killed 84 people in Nice on France's national holiday. Mohamed Lahouaiej-Bouhlel, 31, smashed a 19-tonne truck into a packed crowd of people in the Riviera city celebrating Bastille Day Valery Hache/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis Police work at a site where a Syrian migrant set off an explosive device in Ansbach, southern Germany, on 25 July, killing himself and wounding a dozen others Daniel Roland/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis A Syrian migrant set off an explosion at a bar in southern Germany that killed himself and wounded a dozen others in the third attack to hit Bavaria in a week. The 27-year-old, who had spent a stint in a psychiatric facility, had intended to target a music festival in the city of Ansbach but was turned away because he did not have a ticket Friebe/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis Police officers walk along train tracks in Wuerzburg southern Germany on 19 July, a day after a man attacked train passengers with an axe. German authorities said they had found a hand-painted IS flag among the belongings of the man, an asylum seeker from Afghanistan, who seriously injured four members of a family of tourists from Hong Kong in his rampage Daniel Roland/AFP/Getty Images Terrorism in 2016: Terror attacks in Europe claimed by Isis German police killed a teenage assailant after he attacked passengers on a train in Wuerzburg, southerg Germany with an axe and a knife on 18 July, seriously wounding three people Karl-Josef Hildenbrand/AFP/Getty Images

“So I think that there is undoubtedly significant ongoing risk which is at least as great as the threat to London in the Seventies when the IRA were active on the mainland.”

Warning that children as young 14 were being radicalised by Islamic fundamentalism, he said there was growing concern over the threat posed by British jihadis returning from overseas.

“It’s an enormous concern that large numbers – we know this means at least hundreds of British citizens who have left this country in order to fight – are now returning or may be about to return,” he said.

Mr Hill took over from David Anderson, and was praised by Home Secretary Amber Rudd for his “wealth of experience and legal expertise”.

With a career spanning three decades, the latest watchdog has helped convict the 21/7 bomb plotters, bring Damilola Taylor’s killers to justice and break up numerous terror cells.