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With cameras given access to the prison for the first time, Kemp went on the inside over a period of six months to explore 'how prisoners and staff cope with high-profile inmates, extremists and common criminals living side-by-side'.
Adrian Knight, head of prisoner safety at HMP Belmarsh, said: "We will take anyone. We've had war criminals in here for genocide. There's not one prisoner in the country that we won't take.
"We've got 17 convicted terrorists, 187 murderers, prisoners that have killed three or four people."
In one part of the documentary, Kemp even found himself unable to speak after breathing in a tiny amount of spice residue left in a vape device by a comatose inmate.
According to The Sun, Kemp recalled: "I am rarely lost for words, but as I turn to camera, I have lost the ability to speak.
"My brain has gone blank, my hands are clammy and my mouth is dry. I have just inhaled a tiny amount of spice residue left in a vape by a comatose prisoner.
"This particular version of the drug is known as Man Down - and it does exactly what it says on the tin. It is a potentially lethal combination of aluminium cleaner and insect killer, and the man who smoked it has collapsed.
"Prison officers and medical staff have responded to a Code Blue, where a prisoner has difficulty breathing or is unconscious."
Thankfully, the prisoner was brought round by staff, who used citrus - which can take away some of the effects of the drug.
In the first episode, Knight also opens up the country's only Contingency Suite, a self-contained unit designed to hold high-profile prisoners deemed at risk of suicide or attack by other inmates - which has been home to the likes of Soham killer Ian Huntley, black cab rapist John Worboys and hate preacher Anjem Choudary.
Speaking about one of the prisoners in the Contingency Suite, Knight said: "The windows are sealed so you can't get around the bars.
"[He has] his own shower facilities... It's about what we need to do to keep prisoners and obviously the person down here safe. Or to keep them from having access to people they might be able to influence in some way.
"And then obviously you've got the exercise yard, which is self-contained. Not very nice, but yeah."
Welcome To HMP Belmarsh With Ross Kemp airs tonight on ITV at 9pm.
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