Chief Inspector Pete Dalton from Thames Valley Police said there is a risk of complacency over the current threat.
He said low-sophistication terror attacks such as the atrocities in the UK in 2017 could happen at any time.
He said: “The threat has definitely morphed into that low-sophistication, low-complexity, vehicle-as-a-weapon attack, edged weapon, explosive device, firearm or combination of those. It hasn’t gone away.”
This comes as MI5 warned there could be an ISIS terror cell in every British city.
“There’s still lots of work to be done and sadly it’s only a matter of time before another incident happens”
Ch Ins Pete Dalton
“Complacency is a real risk,” Ch Ins Pete Dalton added. “It’s a real risk in the professional security industry, in terms of budgets and cost. It’s a risk in terms of mindset.
“There’s still lots of work to be done and sadly it’s only a matter of time before another incident happens.”
He said it was “extremely challenging” to secure funding for vehicle barriers at Windsor until the Westminster Bridge attack in March 2017.
Terrorist Khalid Masood was able to mow down pedestrians by exploiting the weakness.
Ch Ins Pete Dalton added: ”Before March 22 2017, I was trying to get hostile vehicle mitigation into the streetscape at Windsor alongside a colleague from the Met, to protect guard change.
“Financially that was extremely challenging, it was a partnership-funded process and if March 22 hadn’t happened, if there had been a six-month lag, that funding wouldn’t have been there. Now that funding is there.
“It’s just making sure that we do put protective security measures in place at the right locations at the right time based against the threat.”
Police and the security services are running more than 700 live investigations and have disrupted 18 plots in the past two years.
Meanwhile, some jihadis are seeking to return to the UK after ISIS is on the brink of collapse in Syria.
Jihadi Jack claims he misses Doctor Who and pasties.
While Shamima Begum, who has recently given birth, said she wants to raise her son in the UK and insisted people should feel “sympathy” for her.