Prison officers say they have been left with no alternative but to work to rule in a dispute over pay.

Staff at Bullingdon Prison, above, in Arncott, near Bicester, have voted to work only their contracted 39-hour-week, after learning that staff at a nearby jail will earn an extra £1,200 a year from January for doing the same job.

The action means inmates will be locked in their cells for longer periods and rehabilitation and resettlement programmes may stop.

Staff at Aylesbury Prison, and Huntercoombe, near Henley, have had local pay allowances increased from £800 to £2,100 and £3,200 respectively. Bullingdon officers will get just £100 more.

Steve Wrighton, chairman of the Prison Officers' Association branch, said: "It's a critical issue in recruitment and retention of staff. The ones we do get are trying to get out.

"This decision has really dented morale. I can't see it getting any better until we have a rate of pay equivalent to the cost of living."

He said staff at the jail cannot afford to live in Bicester. Some are travelling up to 100 miles a day to work and others are sharing houses.

Mr Wrighton added: "Now, we're competing for staff in our own area. It's not a level playing field. This makes our position even worse."

The allowance was introduced last year by the Prison Service Authority, which sets pay levels, to help fill vacancies in the South East.

At the moment Bullingdon has 40 vacancies in a staff establishment of 350.

A Prison Service spokesman said: "The governor and union continue to work together to find a way forward and to ensure that any case for future increases is as strong as can be."