POLICE are investigating an attempt to smuggle heroin concealed in health food into a top security prison in the North-East.

Prison officers at Durham's Frankland Jail discovered 41 grammes of the drug hidden in a package during a routine check of incoming mail at the weekend.

Their suspicions were raised by "unusual writing'' on the package, which was intended for a particular inmate, and the fact that it was incorrectly addressed.

The heroin's estimated street value is £1,200, but it is thought it could fetch about ten times more in prison because of the difficulty in obtaining drugs.

A Prison Service spokesman said: "Vigilant officers became suspicious about the package. They opened it and found a large quantity of heroin. The police were informed and are investigating.

"We are reassured that the vigilance of the staff when going about routine searching of incoming parcels has led to the discovery."

A spokesman for Durham Police said: "It was a brown powder and has a street value of £1,200, but prison values tend to be inflated and it could be worth up to ten times that amount inside.

"Prisons are operated with varying degrees of security, but this is a top security prison, so getting anything in would be extremely difficult and prices would be hiked up accordingly."

Police said their inquiries are at an early stage. They have not revealed where the package was sent from or who it was sent too.

Frankland's inmates include "Dr Death" serial killer Harold Shipman, but the intended recipient is not thought to be a so-called "celebrity" criminal.

The jail has a drug recovery unit designed to help addicted inmates break the link between drugs and crime.

Last year, it was awarded a coveted Government Charter Mark for excellence in public services.

The Prison Service spokesman said the system for checking parcels had proved successful, but he added: "It would be wrong to suggest there aren't drugs in prison.