The multinational security company hired by the government to deport refused asylum seekers was warned repeatedly by its own staff that potentially lethal force was being used against deportees, an investigation by the Guardian can reveal.
Details of how some G4S guards developed a dangerous technique for restraining deportees by bending them in aircraft seats is disclosed in official testimony drawn up by four whistle-blowers from the company.
Their evidence was secretly submitted to the home affairs select committee in the aftermath of the death of Jimmy Mubenga, an Angolan man who died while being forcibly restrained on a flight from Heathrow in October.
The previously unseen testimony reveals that G4S managers were repeatedly alerted that refused asylum seekers who became disruptive on flights were being "forced into submission" with their heads placed between their legs.
The technique, which is strictly prohibited because it could result in a form of suffocation known as positional asphyxia, was nicknamed "carpet karaoke" by G4S guards.
The whistle-blowers also allege that staff were not trained properly, criticised for showing compassion to refused asylum seekers, particularly children, and ostracised if they ever voiced concerns. They state that some guards went years without receiving official Home Office accreditation.
Their evidence contradicts testimony given to parliament by senior G4S executives who were summoned to appear before the home affairs select committee following Mubenga's death. One senior G4S official told MPs during a the hearing in November that he was "not aware" that his staff had ever raised concerns about any aspect of the removals process.
The chair of the committee, Keith Vaz, said he was "extremely concerned" about the allegations, which the committee would review before deciding what action to take. "Where services as important as this are contracted out and where there could be a danger to lives, it is vital that the practices of the company are fully scrutinised."
"If any warnings were given about restraint techniques being used, I would have expected these to have been taken heed of in the first instance."The evidence submitted by the whistle-blowers, who include three former employees as well as the company's existing charter operations manager, provides a detailed record of written and verbal complaints to the company since mid-2004. According to their testimony, G4S received repeated warnings from staff, whose complaints included that training had to change "before there was a serious positional asphyxiation incident resulting in a detainee's death".
One letter, expressing frustration that G4S was failing to take action and allowing inappropriate force to be used against refused asylum seekers, stated: "I urge you meet this problem head on before the worst happens." It warned that bosses of the company were "playing Russian roulette with detainees' lives".
In his evidence to parliament, the letter's author, currently on sick leave from his job as G4S charter operations manager, said:
"I am greatly saddened to say that despite my protestations these illegal and extremely dangerous techniques continued to be used by some who cared little for the welfare and lives of those they had in their custody." He added the dangerous restraint techniques were used for a period "with the tacit approval of senior managers who catastrophically failed to halt its use and spread".G4S discovered after Mubenga's death it had lost its Home Office contract – thought to be worth more than £100m – to conduct overseas removals, but said the decision was unrelated to the asylum seeker's death. The three G4S guards arrested in connection with Mubenga's death have been bailed to reappear next month.
The contract will be taken over in May by a rival security firm, Reliance. Under European employment regulations, Reliance has been compelled to offer employment to all G4S staff involved in removals.
Meanwhile G4S continues to hold contracts with several government departments estimated to be worth £600m. It manages four prisons, three immigration removal centres and escorts around half of all prisoners to and from court.
G4S said in a statement it was aware that allegations had been submitted to parliament, but added that, despite requesting the details, it had not yet received the information and was therefore unable to respond. "We would obviously be keen to investigate these allegations but will not be able to conduct a review or take any action without seeing the evidence."
The company added that appropriate action including disciplinary action is taken when staff conduct is found to have been inappropriate. "The welfare of detainees in our custody is our top priority and we take any allegations of mistreatment extremely seriously."