A controversial Conservative Party political broadcast screened last night, which claimed that two women were raped because of Labour's Early Release scheme for prisoners, was partly filmed at the former Oxford Prison.

The bleak opening scenes were shot in the former jail, now hired out as a TV and film set by the county council.

Without spoken commentary but with atmospheric background music, the broadcast claimed drug dealers, robbers, burglars, and violent criminals were being freed too early, with many then committing further offences.

Among the offences which Tories say would not have happened if the convicts had served their full sentences were two rapes, seven cases of grievous bodily harm and 91 other assaults. Tories say they will scrap the scheme.

Nick Evans, buildings officer for the county council, said: "A film company came on March 30.

"I knew they were making the film for a political party but I was not aware it was for the General Election."

The prison shut in 1996, and plans have been submitted for a major redevelopment which will include a leisure complex and hotel.

Home Office minister Paul Boateng last night condemned the broadcast as "desperate, dire and a damning indictment of the way the Conservatives intend to run this campaign".

He added: "It is negative advertising of the worst possible sort."

Juliet Lyon, director of the Prison Reform Trust, described the broadcast as "scaremongering".