Watch 'Most Haunted': HMP Gloucester - Part 1 - Full Episode

Yvette Fielding assembles her team for a massive two-part Christmas investigation at the foreboding and now disused Gloucester Prison. The vast site is said to be one of the most haunted places in Great Britain, a place that has seen death, fear, pain, suicide and incarceration. A place that is built on the rotting corpses of many prisoners, a place to be feared.

The team's mammoth investigation is split into two parts with the conclusion premiered exclusively on the official Most Haunted YouTube channel.

Yvette starts by telling us a little about the location. We learn that HMP Gloucester was originally built as a county jail. The William Blackburn-designed prison first opened its doors in 1792, and for over two centuries housed murderers, thieves and the violent of every kind.

Gloucester was not just a jail for the convicted to serve their terms, it was also a place of execution. Over 120 judicial hangings were undertaken in the foreboding place over the years, with many of the condemns still remaining buried within the grounds in unmarked graves.

During its operational years, Gloucester Prison has seen riots, violence, death and suicide. In 2003, it was named one of the most overcrowded prisons in the UK, before eventually closing its doors to the criminal justice system for good in 2013.

With so much death sadness and despair, it's no wonder that the former jail is said to be so haunted. The reported paranormal activity includes doors slamming in empty cells, the sound of heavy footsteps walking the corridors and landings, dark figures seen all over the building, and disembodied cries heard in the dead of night.

Yvette and the team hope to find out if these reports are a sign that long-dead inmates still imprisoned in a state of eternal torment are trying to communicate with the living. Could the executed be continuously reliving their final moments, or is this just an old building replaying the past?

Before the investigation got started, Yvette said that walking around the abandoned wings made her feel uneasy. She was joined by the show's resident skeptic, Glen Hunt, who said he agreed that it was an eerie place, but said part of it could be down to what we expect to find in a building like this. He told Yvette, "a lot of it is psychological but that's entirely the whole point of what the building is suppose to fill you with."

Yvette added, "I think when the lights are turned out we're all going to feel a bit apprehensive." They would soon find out.

Having already witnessed plenty of knocks and bangs on their initial walk around, the team switched their cameras to night vision and got started. With such another imposing location to investigate, Yvette decided to stick to the old idiom, "safety in numbers". So she took the whole team to A Wing to start the investigation.

Yvette and Glen were joined by demonologist Fred Batt, Karl Beattie, Stuart Torevell, and camera man Gregg Smith. A Wing proved active for the team as they experienced plenty of unexplained knocks and bangs coming from all around them. The strange noises continued as the team split up and Yvette, Karl and Glen held a vigil on the adjacent C Wing.

Later Glen and Gregg investigated the very creepy former prison workshops, where they thought they heard a sound as if something was thrown. Karl, Fred and Stuart remained on A Wing where they investigated what was once the condemned man's cell. While there in the darkness they heard a whistle, followed by a very loud crash which seemed to be something being thrown near them. This was followed moments later by what sounded like a door slamming.

Meanwhile, Yvette braved a lone vigil in the hospital building, an old wing that used to be the debtors' prison. Despite it being a cold night, Yvette admitted that she was sweating buckets and said, "this is like horror movie 101." But Yvette didn't last long. She left surprisingly calmly after hearing a dragging sound. She said "sorry, no way, get stuffed. There is no way I'm going in there on my own. I'll go back with someone else." Yvette did brave the hospital wing again, this time with hubby Karl to protect her.

The team pushed on into the night, but the rest of their investigation makes up part two, which premieres tomorrow night on YouTube.