A former G4S boss and priest is calling for the end of indefinite detention after a BBC Panorama investigation uncovered 'shocking' levels of abuse and poor behaviour from staff.

Rev Nathan Ward, formerly a senior manager at the security company, told his superiors about the 'poor culture' among workers when he worked at Brook House Detention Centre near Gatwick Airport.

Now a priest in Kent after quitting the company in April 2014 because he 'couldn't cope' and his warnings were being ignored, Ward became a whistleblower for the BBC and is joining others to call for an end to indefinite detention.

Like other immigration detention centres, Brook House is meant to only hold people for a few days but many spent months or even years there without knowing when they will be released. Unlike all other EU countries, the UK does not set a legal limit on the length of immigration detention.

'I call on the Government today to bring an immediate end to indefinite detention setting an upper limit of 28 days,' said Ward, following up calls from MPs in 2015 after a cross-party investigation.

Ward said court approval should be needed for any detention longer than 72 hours and called on the government to focus its immigration policy away from holding people in centres.

'This is not about immigration; it is about ending inhumane practices which are expensive and infective. The UK is a developed nation with high standards - we must demand better than this for our detention centres,' he said.

Ward was joined by Bishop of Rochester, the James Langstaff, who serves as Bishop to Prisons. Bishop James said: 'Based on the news coverage so far around this programme it would seem that this documentary raises serious questions, not just of those who run our immigration detention centres, but more crucially about how we as a society treat people that we don't know what to do with. Those featured in the documentary are human beings with friends, families, and personal stories. And yet the alleged treatment they have received can only be described as inhumane. This system fails not only those directly affected by it, but it fails us as a nation.'

BBC Panorama said it unearthed 'a toxic, brutal and failing environment where self-harming is common place' with footage revealing suicide attempts, drug abuse and evidence of violence inflicted by detainees on each other.

Hardened criminals mix alongside asylum seekers and migrants who are having their applications reviewed and 21-year-old Callum Tulley, who agreed to secretly film what happened during his shifts, said the former 'swarm like sharks around small fish'.

He told the BBC: 'They will just get eaten alive, just snapped up like that.'

In one incident he described how officers treated one 20-year-old detainee who had been on suicide watch for to days: 'This officer comes in and just chokes him basically, and he just exerts all his pressure on from his hands and arms on to this guy's neck, and you see his eyes roll back, you see his eyes roll to the back of his head.'

Responding to the allegations, Home Office minister Brandon Lewis said: 'The dignity and safety of all those in our care is of the utmost importance, and I am taking these deeply concerning allegations very seriously.

'We expect the highest standards and integrity of our contractors at all times, and the Home Office is working closely with G4S to ensure a full investigation is carried out and appropriate action is taken.'

Nine G$S employees from Brook House remains suspended following the investigation and the company says it is looking into the allegations.

Detention managing director at G4S UK Jerry Petherick, said: 'The behaviour shown in the programme is completely unacceptable and not representative of the many G4S colleagues who do a great job, often in difficult and challenging circumstances, across the country.

'We have commenced an immediate investigation into the specific allegations made in the programme.

'I have re-emphasised to staff the importance of speaking out through whistleblowing channels if anyone is concerned about the behaviour of colleagues or standards at any of our facilities.

'We continue to focus on the care and wellbeing of detainees at Brook House.'