STAFF put a pillowcase over an inmate’s head to stop him spitting, a surprise inspection of Bullingdon Prison revealed.

And although the report by the HM Inspectorate of Prisons said the Bicester prison was improving, it highlighted concerns about the use of a body belt and improvised hood to stop the prisoner spitting at staff.

According to inspectors, the incident in July was among some issues that caused “serious concern”.

The report added that the governor had launched an investigation after being told of the incident.

Staff at the prison used force 74 times between January and June 2012, compared with 102 times in the same period last year, the report said.

The jail held 1,087 men at the time of the inspection – almost 25 per cent above its usual capacity.

Last night Andrew Neilson, director of campaigns at the Howard League for Penal Reform, said: “We would hope this incident was an aberration. The use of force by staff should always be carefully managed and used only in exceptional circumstances.”