A police operation was run to reduce drugs, phones and SIM cards being thrown over the perimeter wall at a Doncaster prison.
The operation at HMP Lindholme was aimed at tackling organised crime both inside and outside of the prison walls.
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Patrols of the perimeter fence were stepped up, known hotspots were targeted, search operations were carried out and education sessions were run for prison workers.
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A South Yorkshire Police spokesman said: "During the first seven days of the operation, officers worked alongside prison teams to implement plans aimed at preventing offenders attempting to throw packages into the prison.
"The effectiveness of these plans saw a dramatic reduction in contraband packages in the prison and only one incident reported throughout the operation."
Police Sergeant Kate Leake, who led the operation, said: "Our main aim has been to disrupt and deter organised criminality being facilitated by the provision of contraband items in ours prisons.
"Our improved partnership working with HMP staff has enabled proactive plans to be established and implemented, which have resulted in a reduction in prison criminality and the formation of stronger community relationships. This has also resulted in a demand reduction for the police, prison and medical staff.
"Alongside this targeted operation, we are also working in partnership with prison staff to implement training, update investigation processes and identify best practice methods to increase the opportunities to present those intent on committing such offences before the courts.
"This work will now continue and I hope this sends out a clear message that crime both in and outside of the prison is not tolerated and we will always seek to take action and prosecute those responsible for supplying illegal items, as well as those conspiring to receive the items inside."