Image caption Covert footage was filmed inside Brook House, near Gatwick Airport

The head of a G4S-run immigration removal centre which was the focus of a Panorama investigation has resigned.

Ben Saunders, the director of Brook House near Gatwick Airport, has left the role with "immediate effect".

BBC One's Panorama screened footage from the centre which apparently showed officers bullying and abusing people being held there.

G4S sacked three staff and seven others remain suspended following the programme being aired this month.

The Panorama investigation exposed Brook House as a place where drug use and self-harm were common.

The programme used footage recorded by former custody officer Callum Tulley at the centre, which holds detainees facing deportation from the UK.

He began working there at the age of 18 and told the BBC he was "shocked and disturbed" by what he was seeing and hearing about.

He described seeing people dealing and taking drugs, self-harming and fighting.

"There's a culture of violence at Brook House. It's not just a pocket of officers abusing people behind closed doors.

"People will just speak about it so openly or freely."

Media playback is unsupported on your device Media caption WATCH: What Callum Tulley, 21, saw undercover

G4S said it "immediately" began an investigation following the claims made in the programme.

Mr Saunders is also leaving his role at Tinsley House, another immigration removal centre near Gatwick Airport.

Documents seen by the BBC suggest G4S has been making significant profits from running the two centres.

The Home Office has said it is investigating claims the company has given inaccurate financial information to the department about their costs.

An ex-senior manager for the security company made the claims at the Home Affairs Select Committee earlier this month.

At that same meeting, a G4S executive refused to tell MPs how much profit the company makes from Brook House.

G4S said it had never deliberately given false information.

In a statement, G4S confirmed Mr Saunders' post would initially be taken by interim director Lee Hanford "pending the eventual appointment of a replacement".

Watch Panorama - Undercover: Britain's Immigration Secrets on BBC iPlayer