(Reuters) – British MPs accused outsourcer G4S of repeated failures of detainee welfare safeguards and whistleblowing mechanisms at a secure immigration unit, after physical and verbal abuse by guards was revealed in a BBC documentary.

G4S, contracted by the British government to run the Brook House detention centre near Gatwick Airport in southeast England, earlier this month suspended nine members of staff, three of whom have now been sacked, for abusive behaviour following the documentary. Police are also investigating.

G4S executives Peter Neden and Jerry Petherick gave evidence on Thursday to a cross-party parliamentary committee responsible for overseeing interior ministry matters.

The BBC film, shot with a hidden camera, showed a guard choking a detainee, as well as drug abuse and mistreatment – including mocking inmates who had deliberately hurt themselves – in centres packed with both convicted criminals as well as those whose immigration visas had simply expired.

“You clearly have a system failure to allow these things to happen in the first place,” committee leader and Labour Party lawmaker Yvette Cooper told the G4S directors.

“You have told us nothing that gives us any confidence that you have a strategy for dealing with this or for understanding how it could happen in the first place.”

Neden and Petherick said the company’s whistle-blowing mechanisms had not revealed any such abuses, nor the suspected sale of drugs to inmates by staff. They admitted failures and expressed regret regarding the actions of staff and conditions.

G4S denies, however, that it has a systemic or cultural failure. Another documentary by the BBC in January 2016 alleged staff at the Medway secure training centre for young offenders in Kent, run by G4S, had used unnecessary force and inappropriate language.

Nathan Ward, who worked at Brook House for 10 years and acted as a whistle-blower, told the committee he had “lost count” of the number of meetings and actions he had taken with politicians and executives to address conditions at Brook House.

He said he had received threats following the airing of the BBC programme and had had his car tyres slashed.

The Brook House contract, which executives said was profitable but declined to give full details, is currently in a public rebidding process for which G4S has applied. The result is due to be announced in November.