A major crackdown to dismantle ‘county lines’ drugs gangs operating in Norwich has been pledged with thousands more arrests.

Boris Johnson vowed to "come down hard on the gangsters who are making hell of people's lives" as part of the government’s new 10-year drugs strategy, saying he was "absolutely determined to fight drugs".

Police will get millions in extra funding to fight London-based gangs that exploit young people to traffic drugs to areas like Norfolk.

It will build on Operation Orochi which has seen Norfolk and the Met Police sharing intelligence on drugs gangs and has seen 52 ‘county lines’ closed and 77 people being charged.

It has led to 45 convictions with sentences totalling more than 177 years.

A number of high profile knife crimes including recent multiple stabbings in Norwich that have been linked to county lines drugs gangs.

The £300m gang crackdown will be joined by the "largest ever investment in treatment and recovery", the government said.

The prime minister said he wanted to break the cycle of arresting culprits "time after time" and returning them to prison "again and again" for being involved in drug-related crime, by offering the "humane" option of rehabilitation.

The strategy will expand drug testing on arrest, with police encouraged to direct drug users towards treatment or other relevant interventions.

Judges will also be given the power to order drug tests on offenders serving community sentences for drugs-related crimes, with the prospect of jail if they test positive.

The Matthew Project, which works with people affected by substance misuse in Norwich, said the strategy looked like a “very ‘enforcement’ focused approach”.

Chief executive Andy Sexton said: “We would welcome any emphasis on increasing support for people in recovery to stop relapse and reoffending."

Also included in its strategy is expansion of Project Adder, which has been trialled in Norfolk focussing on treating addicts in order to combat demand for drugs.

It has led to significant success, particularly in parts of Norwich previously blighted by drugs and gang violence.

“Diverting drug users into recovery and treatment will reduce demand for drugs and the criminal activity associated with it in the greater Norwich area,” said a spokesman.

“Being part of this pilot project allows us to be at the forefront of developing a new approach to tackling drug related deaths, the level of drug related offending and the prevalence of drug use in Norfolk.”