County lines drugs gangs could move back to using public transport to move crack and heroin as trains and coaches get busier in the coming months.

Restrictions linked to the pandemic last year forced drugs couriers to use cars as coach services stopped and train services were reduced, making them more identifiable and increasing the risk of being caught.

Police are now monitoring whether the gangs will return to trains and coaches as passenger numbers increase again, allowing them to blend in with crowds while moving consignments of illegal drugs.

Britain’s biggest police force, the Metropolitan Police, has arrested more than 1,000 people linked to county lines gangs since November 2019.

Around 600 of the lines are in operation in England and Wales, down from an estimated 2,000 in 2019, and they are thought to be one of key drivers behind the number of teenage murders in London this year, on course to be a record high.

Deputy assistant commissioner Graham McNulty told the PA news agency: “Unfortunately with county lines we do see significant violence.

“That violence is created because you’ve got young people and gangs often fighting over a territory to sell drugs.

“And they use violence to try and win that territory.

“If people are in debt to them they use violence, and they will use exploitation of young people to get young people to run the lines for them so that they’re forced into undertaking that activity.”

Being forced onto the road network during the coronavirus lockdowns meant older gang members were needed to move drugs, and reports of children involved in county lines going missing dropped during this time.

But it also made gang members easier to track, Mr McNulty said.

“By moving to the road network that did give us other opportunities.

“It gave us the opportunity to look out for vehicles, to observe vehicles and understand the routes that people were taking,” he said.

“Rather than when they’re on a train or a coach and they’re slightly more anonymous to us.”

He added: “We’re watching closely to see how the county lines drugs distribution model changes as more people are back into the workplace and transport routes are busier.”

The Met’s latest raids targeting county lines were carried out on Monday morning, with three people arrested in Essex and London.

A 40-year-old man was held in Francis Avenue, Ilford, Essex on suspicion of attempted murder, while two other people, a 20-year-old woman in Waltheof Gardens, Tottenham, north London and a 26-year-old man in Hounslow, west London, were arrested on suspicion of being involved in the supply of class A drugs.

Commissioner Cressida Dick said: “One of the suspects arrested this morning was wanted for attempted murder linked to county lines activity.

“It could not be clearer that county lines brings with it serious violence and harm to communities not just within London, but across the country.”

The Met is increasingly aiming to charge gang bosses with modern slavery crimes for the exploitation of young and vulnerable people, as well as drugs offences.

Since November 2019, 21 defendants have been charged with 38 slavery offences and nine convicted of human trafficking offences.

Dame Cressida said: “Our recent use of modern day slavery legislation against those exploiting young and vulnerable people has resulted in significant custodial sentences.

“This type of conviction also enables us to place tight restrictions on these individuals once they are released from prison.

“We’re also looking really closely at how we ensure those involved in county lines do not make a penny from it.

“They cannot profit from the misery they cause to the most vulnerable in our society and the wider public.”

The force has also used automatic number plate recognition to track violent offenders and suspected county lines criminals in Operation Pandilla.

Forty-six people were arrested and 10 weapons seized as part of intensified action last week.

In another day-long operation in Croydon, Sutton and Bromley on Saturday, officers stopped 367 vehicles, with 26 seized, eight people arrested and stolen goods worth £30,000 recovered.