The governor of a Teesside prison says criminals are deliberately allowing themselves to be sent to prison - so they can sell drugs on the inside.
Matt Spencer, of Holme House prison in Stockton, said there had been about 30 such cases in the past year.
Police said they were aware of the activity and warned they were "on to" those who carried it out.
The prison said intelligence from the courts and police had helped them to identify those responsible.
Mr Spencer said criminals would try to have themselves sent to prison by "causing chaos in court" or committing a crime to be specifically brought into prison.
Det Ch Insp Rob Donaghy said: "We are aware that they get arrested for minor offences and deliberate breaches of orders to try and take drugs into prison and try and supply the drugs inside the prison.
"What I would say to those people are that we are on to you, we do have intelligence and we work closely with the prison."
Drugs worker Tina Williams said the authorities must stay vigilant.
"We have got to stop the availability on the streets and in prison.
"If you don't do that, all the billions you are pumping into treatment services is wasted."