by Alison Hodgkins-Brown, Gareth George, Richard Martin and Oliver Rogers
The Severalls Hospital site is around 150 acres
A conservation group has raised concerns about the state of repair at the former Severalls mental hospital in north Colchester.
BBC Essex gained exclusive pictures after entering the site and showed them to the Save Britain's Heritage group.
William Palin, the secretary of the organisation, told BBC Essex: "I'm absolutely horrified. What we have is a scene of desolation."
The hospital closed in 1997 but a few buildings are still used by the NHS.
William Palin looked at the pictures in a BBC studio and said: "A beautiful complex of buildings, which have been systematically destroyed, because the site hasn't been secured from vandals."
Some buildings on the site, such as the water tower and the main reception are listed because of their historic importance.
In a statement to BBC Essex, the North Essex Partnership NHS Foundation Trust, which own most of the site in Colchester, said: "Severalls Hospital is private property and access is strictly prohibited.
Evidence of graffiti, vandalism and fire damage are visible
"Breaking into this restricted area is a crime and the Trust will strongly consider formal prosecution for any illegal entry," they added.
The North Essex Partnership NHS Foundation Trust had been trying to sell the Severalls site to property developers, with the latest deal collapsing in 2007.
Colchester's Liberal Democrat MP, Bob Russell, also viewed the BBC Essex pictures.
"When I see the pictures I've just seen I look back to the years of my youth in Mile End, which is where Severalls Hospital is located," he said.
"I can visualise wonderful buildings, a caring community and I now see those happy reminders obliterated by incompetent management, by those who are supposed to be looking after public assets today," added the MP.
Built in 1913, Severalls, at its peak treated over 2000 patients and closed in 1997.
Below are exclusive pictures taken by BBC Essex at the Severalls Hospital:
Tell us your memories of Severalls Hospital.
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Emily writes, "I am utterly horrified on how the hospital has become. I haven't been to Severalls as a trespasser, but a lot of people have. I know a lot of people would have loved to have saved Severalls from what it has become.
"I know people have come along and killed the spirit that was Severalls, and it just feels like that the North Essex Partnership NHS Foundation Trust have given up on Severalls, because no one has come and bought it.
"Thank you for putting up the story of Severalls. I hope that it doesn't encourage other people to come and smash it up more.
"It would break my heart if the building fell, because I would love to show the world Severalls from what it was then, rather than what it is today, and plus most of my family were at Severalls."
Luke writes, "Just like to say what a great story about the hospital and I'm glad your team went in to the hospital to show everyone what the health trust has done to the hospital .
"I used to work at Turner Village hospital where most of the residents came to, yet again this was closed in time.
"It is such as shame that Turner Village and Severalls hospital were both closed as this was the residents' home and was meant to be for the rest of their lives.
"If I had my way I would put them all back as mental health hospitals so residents can live in a safe warm and caring place."
Bill from Colchester writes,"I don't understand why anybody should be surprised that the buildings are in a state of disrepair having been abandoned 12 years ago.
"Why would you spend money repairing a leaking roof when it will be demolished when redevelopment takes place in the next few years.
"Not only that, I would rather the money was spent on health provision rather than patching up roofs of abandoned buildings.
"Most of the buildings were never worth saving except in the eyes of a few anoraks who seemed to think they were of some merit.
"Don't forget there are lots of people who would cheer when these buildings are demolished to erase the painful memories there have either personally or in their family of what took place there."
Alan writes, "As an ex-employee of the precursor of the current health authority I am disappointed but not surprised at the condition of the old Severalls Hospital.
"Ever since the early planning stages of the current Colchester General Hospital the local managers did not want this site."