Updated 21:08, 2 January 2012 - Further information on and image of Phillip Westwater

A convicted killer dubbed the Black Dog Strangler has escaped from a secure hospital.

Police said that Phillip Westwater, 44, fled St Nicholas Hospital in Gosforth, Newcastle, at 10am on Wednesday after asking to go to the toilet.

He was detained indefinitely under the Mental Health Act following a pub fight in 1989, then strangled fellow patient Derek Williams at Ashworth Hospital, Liverpool, with his dressing gown cord.

He admitted manslaughter on the grounds of diminished responsibility, having become convinced his victim had turned into a black dog.

Northumbria Police, who released a photo of the strangler showing his tattooed, muscular arms, said the public should not approach Westwater.

Westwater is shown smiling in a dark vest top as he displays a tattoo on his right upper arm of a woman stripping off, and something resembling a bird of prey on his lower arm.

phillip westwater

Northumbria Police have warned the public not to approach Philip Westwater

A spokesman said: "Officers are making inquiries into this individual and any risks he may or may not pose.

"In the meantime people are asked to contact police on the 999 emergency number if they see him and not to approach him."

The police spokesman added: "Mr Westwater was being escorted in the hospital when he asked to go to the toilets, from where he escaped."

Westwater is described as white, 6ft and of slim build, with brown/grey hair.

He left his clothes in the toilet so police have no description of what he is wearing.

Westwater, from Newcastle, married a nurse while he was a patient at high-security Rampton Hospital in 2008.

He and his bride, reported to be Claire Dudley, wed in a social club at the Nottinghamshire hospital.

Nottinghamshire Healthcare NHS Trust said the right to marry was enshrined in the 1988 Human Rights Act.

A hospital spokeswoman denied the couple could consummate their marriage while he was being treated there.

In 1989 Westwater left a drinker paralysed for life after slashing him across the throat with a shard of glass in a pub fight. He killed Williams at Ashworth Hospital the following year.

Before being treated at Rampton, Westwater had also been a patient at Broadmoor.

St Nicholas Hospital in Newcastle is considered a medium-security unit.

Westwater will have undergone a risk assessment before he was escorted by a member of staff, a Northumberland Tyne and Wear NHS Foundation Trust spokesman said.

"Patients in receipt of hospital care routinely undertake periods of planned or escorted leave as part of their treatment plans, which are designed to help in their recovery.

"Before being granted leave, all patients are rigorously risk- assessed.

"In the rare event that a patient does go missing, we have agreed protocols in place with our colleagues at Northumbria Police to ensure that patients are returned to hospital as quickly as possible."

Westwater was being escorted from his ward to a restaurant in a separate building - but within the hospital site - when he went missing.

It is understood police will have been in contact with any friends and family the patient has living in the Tyneside area.

As he was detained under the Mental Health Act, Westwater will have been treated as a patient rather than a criminal, with emphasis on improving his condition.

Prior to any period of escorted leave, he would have been assessed by his consultant psychiatrist, a psychologist and the nursing team.

As he was previously treated in high security hospitals prior to moving to the Newcastle unit, it is understood medics will have considered his condition to be improving.