Police say new tactics have enabled them to drive the expansion of ‘county lines’ drug dealing into reverse, and have vowed to eradicate it from the country’s worst-affected area.

County lines – whereby drug-dealing gangs from cities expand their operations to other areas – had been growing every year, with rural areas such as Norfolk plagued by drugs from London and serious violence. Gangs had become so comfortable they were sending out “Happy Christmas” messages to their clients.

Under the tactics, escalated during the coronavirus lockdown, officers go after those controlling the lines from London via their pay-as-you-go mobile phones rather than just chasing the runners sent to rural areas.

In Norfolk, the runners are usually teenagers who transport drugs in clingfilm wraps within their body. Cash is taken back to London in the same way.

So far, 30 out of 75 lines in Norfolk have been shut after those controlling them were traced and arrested in London, police say, with the closed lines responsible for half the drugs sold. Det Insp Robin Windsor-Waite, the officer leading Norfolk police’s efforts, told the Guardian: “It is a massive rollback.”

Norfolk is the area in Britain with the highest number of recorded crimes linked to county lines, with hotspots in Great Yarmouth and King’s Lynn, and police say they have rewritten the rule book on how to tackle it.

Windsor-Waite said: “As those controlling the networks are commonly based outside the county, they may have a feeling of impunity, believing they’re beyond our reach and being careful not to attract the attention of their home force. To successfully tackle county lines criminality, we need to arrest the controlling minds rather than the mules and street dealers.

“In the majority of cases, the arrest of the line controller terminates the line – and the risk associated with that line. Prior to this operation there was a degree of resignation to the continued exponential growth of county lines within Norfolk. The outlook has been transformed and our ambition is to completely eliminate the county lines business model from the county.”

The tactics have led to arrests being made in London since December. The Home Office provided extra money for the Met to act on intelligence.

Since November, 146 London-based alleged county line holders have been charged with selling class A drugs such as crack and heroin across Britain – in Scotland, Surrey, Kent, south Wales, and Devon and Cornwall, as well as Norfolk.

The Met’s deputy assistant commissioner Graham McNulty, the national police lead for county lines, said: “They probably felt they were doing something that was low risk, high reward. And what we are starting to do is turn it on its head. Suddenly county lines becomes a high risk issue for them, and the reward relatively low.”

On the 146 arrested, 69% had gang connections, with most having previous convictions for drugs or carrying weapons, McNulty said. More than 70 alleged associates operating from the capital have also been arrested, while forces in Merseyside and the West Midlands have also been targeting county lines dealers based in their areas.

The dealers employ a range of tactics to evade police, Windsor-Waite said, using children in the belief they are less likely to be stopped, while gangs operate a “just in time” supply chain, eschewing transporting large amounts of drugs at once. The usual method of transportation is anal concealment, known as plugging.

Windsor-Waite said: “The crack and heroin is usually prepared for sale in London before being exported to Norfolk. The drugs are divided into individual £5 or £10 street deals and bundled into £1,000 packages, wrapped in clingfilm and ‘plugged’ in the courier’s rectum. The cash proceeds are carried in the same way … Sadly, this has become ‘normalised’ amongst the children and young people involved.

“This is driving the exploitation. If you move small amounts of a commodity, it’s a lot safer, but it needs lots more people. You need to move drugs every day or two.”

Norfolk police chiefs say those involved in county lines changed tactics towards the end of 2019. Bad publicity about cuckooing – taking over properties from the vulnerable to use as a base – led gangs to cajole and bribe rather than threaten, and there was an increased attempt to recruit and use local children.

The force adopted behavioural science tactics developed to fight terrorism in order to spot child victims arriving at Norfolk’s train stations from London. Ch Supt David Matthews said: “For a county force seen as an easy target, we have probably made the environment as hostile as we can.”

Norfolk’s chief constable, Simon Bailey, warned that police can only do so much: “While there is demand, there will always be a supply. Somebody will take that risk. That is why other agencies are working with police to deliver a comprehensive rehabilitation programme for people for are addicted to class A drugs, to break the habit.”