Doncaster's prisons have been targeted by police in a crackdown on visitors smuggling items into the jails' inmates.
An operation carried out by officers at HMP Lindholme and HMP Moorland was the first what will be a number of days of action to stop visitors bringing in contraband.
Police say the operation resulted in a large number of of vehicles swabbed and testing positive for drugs. As a result of those test, their visits were cancelled.
Officers said two people were dealt with for drug possession and one was arrested for drug driving.
More operations are set to be run in the coming weeks.
Doncaster Police Supt Neil Thomas said: "We are trying to deter people from bringing in illegal items into prison. We are going to be be running a series of operations around the prisons in Doncaster aimed at engaging with visitors and stopping and dealing with those who bring in illegal items like drugs and mobile phones.
"This is something that we intend to do on a regular basis, and it is something that we have not widely publicised.
"Part of the operation is the deterrent factor. No one is suggesting everyone who visits prison is a criminal, but there are some who pass illegal contraband."
The operation at Lindholme and Moorland was carried out on October 16.
The operations will be unannounced and potentially could be carried out at any of the borough's four prisons. The borough is home to HMP Doncaster. HMP Moorland, HMP Lindholme and HMP Hatfield.
In the past, the borough's jails have also seen incidents of people throwing items into the prisons' grounds, and event drones being used to take items into the grounds, but Supt Thomas said that had not been widespread. Some cases had involved drones crashing. Officers had worked proactively to deal with the issue, he said.
The action came just four days after a targeted day of action on October 12 netted more than 1kg of cannabis and a large quantity of cash at Lindholme Prison. Outside of the jail, police also executed a number of search warrants at properties across the town.