An armed robber who attacked a shopworker with an iron bar has been spotted on the run in Oxford after walking out of an open prison.

Andrew Ivison was seen in Cowley, on Saturday morning, hours after escaping from Spring Hill Open Prison just months into a six-year prison sentence.

The 32-year-old, originally from Barton, had only been sent to the Buckinghamshire open prison two weeks ago after originally being imprisoned at the higher security HMP Bullingdon, near Bicester.

He was jailed after stealing cars from the John Radcliffe Hospital, where he worked as a cleaner, and driving them to rob small shops, armed with knives and an iron bar.

Staff reported Ivison missing during a roll-call at 8.30am on Saturday, less than an hour after a member of the public saw him in Hunter Close, Cowley. He was last seen at the prison at 11.30pm on Friday.

Ivison was sentenced in May last year to six years after admitting robbery, attempted robbery and asking for 39 further offences (including two robberies) to be taken into account.

He was captured on CCTV bashing a 17-year-old shopkeeper with an iron bar at Co-op in Banbury Road, Kidlington, before stealing £716 from the till in December 2004. The following month he leaped across a counter brandishing two knives while wearing pink rubber gloves at Costcutters in Old Marston Road in Oxford.

Oxford police spokesman Tim Wiseman said: "Ivison has a history of involvement in drugs and has been violent towards police officers.

"We have been in contact with his known associates, friends and family throughout the city. If a member of the public does recognise him we would urge them not to approach him personally but to contact the police."

Ivison was transferred to Spring Hill Open Prison from Bullingdon after a Home Office risk assessment.

He was due to be released from jail in 2009.

Police have described him as 5ft 10in tall, with blue eyes, dark brown cropped hair, clean shaven and of medium to slim build.

HMP Spring Hill is a category D open prison near Aylesbury and a former M16 base.

A Prison Service spokesman said: "Open prisons play a vital role in the resettlement process. The Prison Service tries hard to prevent an abscond or escape from custody and those that do occur are always fully investigated.

"The prisoners are thoroughly risk assessed before being deemed suitable for open conditions.

"Where a prisoner is put in open conditions it inevitably entails putting an element of trust in a prisoner, and unfortunately some abuse that trust."

In the 12 months to April, 34 prisoners fled Spring Hill, the spokesman confirmed.

Anyone who sees Ivison can call police on 08458 505505 or Crimestoppers on 0800 555111.