A frail great-grandfather was able to walk out of a secure hospital ward and wander the streets late at night in the freezing cold and rain.

Seriously ill John Langridge, 78, managed to slip out of a high dependency ward at Kent and Canterbury Hospital unnoticed – despite the doors being locked for his own safety.

A taxi driver found him drenched in the city in a confused and distressed state – and was so concerned for his welfare he called police.

Mr Langridge’s furious family said it was a “miracle” he did not die and demanded answers from the hospital.

His son, Christopher Langridge, from Bromley, said: “The first we knew was when a member of staff rang my sister Kay to say, ‘I’m sorry, we’ve lost John’.

“It wasn’t the best choice of words because for a moment she thought he had died until it was explained he had disappeared.”

A disorientated Mr Langridge, of Grafton Rise, Herne Bay, left through a locked door, but hospital bosses admit they do not know how.

When he was found, he was wearing just a polo shirt and tracksuit bottoms. Temperatures were near-freezing and it was raining.

He was returned to the hospital’s Invicta Ward, but Christopher, 47, and sister Kay Dale, 50, who lives in Herne Bay, said it was “incredible” that he was able to dress himself and walk out of the building without someone raising the alarm.

Christopher said: “It was freezing cold and wet and frankly a miracle that in his frail condition he didn’t die.

“He had a urinary infection which had made him delirious and confused and probably caused him to get out of bed and try and get home.

“Apparently he was let out by a cleaner, but how can it be an hour before a patient in a high dependency ward is noticed missing?

“We just find it incredible and think it needs to be highlighted because it could have ended in tragedy.”

Mr Langridge, who is a retired civilian prison service worker, has since been transferred to St Thomas’ Hospital in London for heart surgery but is currently unable to have the operation because of an infection.

Giselle Broomes, the hospital’s divisional director for urgent care and long-term conditions, apologised for the blunder, which happened on February 24.

She said: “We are sorry for any distress caused to Mr Langridge and his family.

“It was freezing cold and wet and frankly a miracle that in his frail condition he didn’t die" - Christopher Langridge

“Mr Langridge was properly assessed by the ward and a decision was made to lock the ward doors for his safety.

“When staff realised he was not in the ward, staff instigated our standard procedures in situations like this.

“They called the police to notify them and Mr Langridge was safely returned to the ward within an hour.

“Our investigation was not able to identify how Mr Langridge was able to leave the ward.”