A woman’s life was saved after she was woken by police in the middle of the night and taken to hospital for urgent treatment.

Hazel Boater, 74, was unaware that tests carried out on her earlier in the day had revealed she could suffer a major heart attack at any moment because of life-threatening amounts of potassium in her blood.

When the hospital couldn’t contact her or husband Wally at their home in Wheatley, they asked the police to go round.

Wally, 76, was woken at about 1am by officers. He said: “They were most insistent that they came up to see if she was OK.

“I think they were expecting to find her dead as it can bring on a massive heart attack.

“I thought it was a hoax at first. I could not imagine what they wanted. If they could not have raised me, would they have knocked the door down? I cannot say.”

Mrs Boater was taken to Oxford’s John Radcliffe Hospital in an ambulance and stayed there for three days.

She said: “It was very frightening. I am just totally amazed with all of it. You do not expect it. It was such a shock.”

Tests were carried out on Tuesday, March 23, as a part of her treatment for liver disease.

She went home after the tests and said that she had felt fine when she went to bed that evening.

But Dr Roger Chapman, a liver specialist who treated Mrs Boater, said the high level of potassium in her blood was a side-effect of the medication she had been taking.

Dr Chapman said: “It was very serious and very urgent. The level was very high and could have caused an immediate heart failure.”

Mr Boater said she had been taking the pills since December last year and that her dose was increased in January.

Police intervention is extremely rare, but the hospital explained there had been no other way of contacting the Boaters.

Mr Boater said he and his wife must have slept through the sound of the telephone ringing.

He said: “I consider her very fortunate. We are very fortunate to have the John Radcliffe just round the corner. They are just kindness themselves.”

He also said he was extremely grateful to staff at Moreland House Surgery, in Wheatley.

He said: “I thought that it would be nice for the people in Oxford to know that things do go right and there are people out there that care for you.

“I take my hat off to the John Radcliffe and I really think they must have saved her life.”

A Thames Valley Police spokesman said: “We were contacted by staff at the hospital. They needed to speak to a woman and they could not get hold of her. We went round to see if they were okay.”