A police force has said it would struggle to provide the response to a terrorist attack that the public would expect because of cuts.

A report from Avon and Somerset constabulary says the force has reached a “tipping point” because of financial pressures and an increased workload.

The report says: “In the aftermath of Manchester, Westminster, London Bridge and … Barcelona, the public have a heightened expectation of policing response that would be very difficult for us to deliver in significant provincial cities such as Bristol and Bath.

“Individuals from the south-west region, some of whom are socially isolated and vulnerable, have travelled or expressed a desire to support Islamic State in Iraq and Syria, while others represent a threat as potential ‘lone actors’.”

Terrorism plots foiled in the region include that of the former public schoolboy Andrew Ibrahim, who planned to carry out an attack at a shopping centre in Bristol.

“A reduction in current funding is likely to mean reduction in prevention activity delivered by our neighbourhood policing teams,” the report says.

“At the same time, domestic extremism is still an ongoing and complex threat. Extremist rightwing behaviour is currently characterised by lone actors attempting to incite anti-Islamic hatred while extreme leftwing activists retain the capability and intent to conduct further attacks within the force area. Effective community engagement by neighbourhood officers is critical in gathering the intelligence that uncovers such plots.

Since the government’s first comprehensive spending review in 2010, the report says, the Avon and Somerset force has made savings of £65m, with 655 fewer police officers. It will have to find a further £17m by 2021-22 to balance its budget.

The report warns: “We now face a tipping point. We cannot sustain further funding cuts without extremely serious consequences.”

Other areas flagged up in the report include management of offenders and the increased workload dealing with people with mental health problems.

The report says that by May 2017, there were 1,926 registered sexual offenders in the area, a number that had been increasing by 10% a year since 2007. The force currently manages more than 11,000 offenders. Another almost 2,000 “high risk” individuals, including domestic abusers, violent offenders, sexual offenders, robbers and burglars, are not subject to formal management.

More than 50,000 police hours were spent on missing people and mental health issues last year.

The chief constable, Andy Marsh, said: “Our continuing ability to safeguard communities, protect the vulnerable, and manage major incidents of this kind is being severely tested. It’s simply not sustainable. There are serious choices to be made.”