National security is being endangered by cuts to local policing, which amount to a potential disaster in the fight to stop Islamist and neo-Nazi attacks, according to one of Britain’s leading counter-terrorism police officers.

Neil Basu, senior national coordinator for counter-terrorism, told the Guardian that two decades of progress in neighbourhood policing were at risk and that withdrawing police on the ground would mean losing the relationships and trust that yield crucial intelligence.

“When we don’t have those people we will become so divorced from the frontline, and the frontline of communities, that [it] will be a disaster for policing in this country,” Basu said. Asked whether it would threaten national security, he added: “Yes, because where’s the intelligence coming from?”

Basu said the spate of attacks in Britain this year could happen again and that the threat of both Islamist and extreme rightwing attack was growing, with the two sets of violent extremists even feeding off each other.

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The senior Met officer said that Britain could not arrest its way out of the high level of terrorist threat by building a “bigger and bigger [counter-terrorism] machine”. The country had to build confidence and trust among communities and redouble efforts to prevent young people from turning to terrorism.

He added: “That connection happens on the ground and that connection is fast disappearing in policing. All the work we’ve done over the last 20 years to put neighbourhood policing back on the map ... is in danger of disappearing. For me, that is a national security issue.”

Asked if the funding cuts the government enacted as part of its austerity drive were having national security consequences, Basu said: “As the senior national coordinator for counter-terrorism the ‘local to global’ thing is incredibly important for me.”

“Local to global” refers to the idea that Britain’s counter-terrorism machine can connect communities, via neighbourhood officers, with specialist police officers and counter-terrorism agencies in the UK and overseas.

Basu said: “The reason we are able to do that in this country without creating shockwaves is because we are not an invading army. We don’t police by coercion, we police by consent. I don’t win that trust and confidence – it’s all the local bobbies on the street who win that trust and confidence.”

At least one plot was thwarted earlier this year because of a tip-off from within the Muslim community and came hours before the alleged terrorist was planning to strike. He said this was the result of trust and confidence in the police from Muslim communities, though he acknowledged that the trust level could be higher.

He also criticised a government decision to cut police funding to specifically fight terrorism. A planned funding cut of 7% was based on the lower level of threat in 2015, he said. “The threat has changed ... It went absolutely stratospheric.”

His warning chimes with comments from the Met commissioner, Cressida Dick, and other senior police leaders, and comes ahead of the government’s budget on 22 November, with ministers facing demands for extra funding for policing, the health service and defence, among others.

Facebook Twitter Pinterest Cressida Dick, Met police commissioner, has warned that police cuts will hit efforts to tackle violent crime. Photograph: Victoria Jones/PA

Basu said the five attacks and seven plots that were disrupted were part of a change of terrorist tactics and tempo which surprised the counter-terrorism experts at Scotland Yard and MI5. “ We were expecting the military push on Mosul and Raqqa to defeat Isis and [Islamic State] to lash back, and we were expecting them to send fighters over here.

“What I think we’ve underestimated is the people here who are willing to stand up. So Isis change their tactics [and] basically said you don’t need permission from us ... attacking where you live is perfectly acceptable. They put out loads of instruction and have been doing so for 18 months.”

The first attack on 22 March saw Khalid Masood mow people down on Westminster Bridge, stab a police officer and attack the Houses of Parliament. It was a seminal moment which showed would-be terrorists that Britain’s defences could be breached, Basu said.

He stressed that as part of fresh counter-terrorism measures the government has been asked to consider higher sentences for those convicted of spreading or being in possession of terrorist propaganda because Isis was changing again. “[Islamic State] will be defeated as a military and territorial presence. They will become an ideological and virtual presence.”

He criticised a judge who this week did not jail a woman caught with online terrorist material, which Basu said had contained extremely violent Islamist propaganda. Basu said: “If you are distributing material, including instructions to commit terrorism, for me that’s like having a knife or a gun.”

He said police had pressed prosecutors to appeal the sentence and added: “In every terrorist case we’ve got we have found the downloading of material,” adding that it was a precursor of terrorist attacks and tougher sentences were needed because police were arresting suspects earlier.

A Home Office spokesperson said it had put extra funding into counter-terrorism, adding: “We committed in 2015 to increasing the money spent on counter-terrorism by 30%, from £11.7bn to £15.1bn, over the five years to 2020.

“We have also protected overall police funding in real terms, are providing £144m to increase armed policing capability in order to respond more quickly and effectively to an attack and are recruiting an additional 1,900 officers at our security and intelligence agencies.”