A BBC Panorama programme filmed undercover at the Brook House detention centre. BBC

Undercover footage taken at a G4S immigration removal centre allegedly shows a detainee who had self-harmed being choked and mocked by security staff.

BBC's Panorama broadcast the documentary detailing the alleged abuse at the Brook House facility, near Gatwick Airport, on Monday (4 September).

The programme claims to have found the centre rife with drugs, including synthetic cannabis Spice, as well as "widespread self-harm and attempted suicides".

Panorama also reportedly uncovered a culture of abuse that has led to the suspension of nine members of G4S staff, pending further investigation.

The footage allegedly shows a detainee being choked by staff and the mocking of detainees who were receiving medical treatment after self-harming or taking drugs.

One incident at the centre broadcast by the programme shows disturbing footage of a detainee self-harming by trying to self-strangulate and putting a mobile phone battery in his mouth.

A detainee custody manager at the centre allegedly remarked: "Plug him in and he'll be a Duracell bunny", before adding: "If he wants to suck on a battery, he can suck on a battery. If it's what he wants to use as his dummy, it's fine, I'm happy with that."

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A man struggles after allegedly taking Spice at the centre. BBC

Later during the same incident it is claimed that the detainee was being physically restrained and choked.

Panorama's undercover reporter said the G4S employee: "basically stuck both of his fingers into his neck, and he was pushing so, so hard I could hear the detainee trying to gasp for breath".

The Brook House facility is one of two immigration centres run by the security firm in the UK and has capacity for 508 adult men.

Those held there include foreign national offenders, asylum seekers and people who have over-stayed visas. Jerry Petherick, managing director for G4S custodial and detention services in the UK, said: "The company investigates all complaints and has confidential whistleblowing channels for staff.

"There is no place for the type of conduct described in the allegations anywhere in G4S and it is not representative of the many G4S colleagues who do a great job often in difficult and challenging circumstances."

The hour-long programme featured a claim that management at the security firm were told three years ago about a cabal of officers mistreating detainees at the centre.

Opened in 2009, Brook House was described as "fundamentally unsafe" a year later in a report. Then in 2012 inspectors found that "significant concerns" remained about the centre.