Abandoned and derelict hospital sites from the old Epsom cluster have become a treasure trove for some, and completely lost their value for others.

In the past decade a group self-entitled “urban explorers” has been visiting the decaying hospital sites, usually after dark, to research and take pictures.

It’s all part of an obscure hobby which has grown in popularity in the last 10 years.

Thrill-seekers, photographers and architecture enthusiasts spend their free time infiltrating the decaying and historical buildings, which are strictly off-limits to the public.

However, residents have condemned their activities, and accused them of playing stunts and vandalising whatever is left of the old hospital cluster.

West Park Mental Asylum, which has had sections closed down in the past two decades, is one of the urban explorers’ favourite sites.

A resident, who did not want to be identified, said: “West Park Mental Asylum in Epsom is being targeted by the Urban Exploration Group and other groups in the UK.

“The place is being broken into on a weekly basis, stunts are being performed, vandalism is being carried out, along with theft and graffiti and soon there may be arson.

“West Park has one of the only padded cells left in the UK. It’s a historical treasure and it’s just being left to be vandalised.”

However, while vandals may roam the old hospital sites, a photographer who does urban exploration has defended himself and other “explorers” from claims of vandalism.

The local snapper, who takes part in urban expeditions under the alias Midnight Runner, said: “I, like many other explorers, have a keen interest in architecture.

“We have a respect for the history of buildings and sites we explore that others don’t.

“I have been all over the country exploring and not once have I, like all the other explorers I know, ‘broken in’ or ‘vandalised’ a building.

“We have encountered many kids vandalising sites, and the majority of the time told them to go.

“When I see a report made by other explorers explaining somewhere has been vandalised through arson or just plain old trashing the place, it angers me that ‘we’ – the explorers – tend to get the blame, because we are the only ones known to be in these sites.”

Midnight Runner has documented many places through photographs and reports in which he describes his trips.

He said: “Many of us have taken our own time and researched all these places for the following generations, to see what sort of heritage they come from through the architecture of before.

“Nowadays there are a lot of buildings made up of glass and steel – no soul, no sign of what made Britain great.

“There is an overused quote for exploring – ‘take nothing but photographs, leave nothing but footprints’ – as overused as it is, this is what we base our exploring on.”

A spokeswoman for Surrey and Borders Partnership, which runs the still active parts of West Park, said: “We have all sorts of security measures in place.

“They are trespassing on private property, and their activities are illegal."