Hundreds of foreign national prisoners are being held indefinitely, sometimes for years, when they can’t be removed from the country.  With no time limit on immigration detention powers, judges and the Home Office are operating within what one lawyer described to me as ‘a culture of indeterminate detention.’

It’s a story that is little known outside the usual circles of lawyers and campaigners. Terror suspects held for 28 days won public sympathy, as did those on control orders. But foreign prisoners, it seems, are a difficult cause.

The power to detain someone for immigration purposes is, in theory, limited in law. Since 1971, the Government has been able to hold someone while it tries to remove them from the UK. These powers were extended after the foreign prisoner debacle in 2006.

Charles Clarke lost his job when it was revealed that around a thousand foreign national prisoners had been released when their sentences ended, without being considered for removal. The Home Office came under huge pressure in the press and Clarke’s successor, John Reid, promised a new, tougher regime.

In 2007 the law was changed so that the Home Secretary could detain someone while considering whether or not to remove them.  This allowed the Government to detain foreign prisoners as soon as a sentence finished, even where there was no deportation order in place.

It’s probably true that most people in the UK, if they were asked, would say that foreigners who commit crimes should be made to leave.

But there were and still are major problems with this approach. Many people simply cannot be removed from the UK, though the reasons vary from case to case.

Despite being known as ‘foreign prisoners’ some have lived legally in the UK for many years. Somalis, for example, who were given  as children but then commit offences as adults.

Lawyers are fighting cases like these on the grounds that deportation would be a breach of a right to family life, under Article 8 of the European Convention on Human Rights.

In February a Supreme Court judgement supported this.  A woman, known as ZH, was told she could stay in the UK because she has two children here and because those children are British.

While these cases are fought out in the courts, the Home Office wants to keep people locked up, no matter how long it takes.

I interviewed a North African national, S, who refused to cooperate with the UK Border Agency when they tried to remove him. He had leave to remain but after a drug related jail sentence was given a deportation order.  His battle to stay led to him spending a further three years in detention.

With good legal help, S not only won compensation for unlawful detention but has also just won back his indefinite leave to remain.

One of the things the judge discovered was that the Home Office had lied in his bail hearings, claiming to have submitted a request for travel documents to his embassy when they hadn’t actually done so.

He speaks reverentially of his lawyers, telling me: “While I was an immigration detainee in prison I didn’t know I had the right to apply for bail. I really believed the UKBA could hold me there for as long as they wanted. I thought they had the power to do that.”

So what does the Home Office say about this? Their line is that people are only detained for long periods where they are resisting their own removal.

But I met people who had spent years in detention despite being very willing to return home. Iranians or Eritreans for example, whose embassies won’t provide travel documents.

One man I met, Ahmed, is lost now, floating in a world without citizenship of any country. The Home Office say he can’t stay here, but the Iranian authorities won’t let him go back there either. After two years in detention he is now living on section 4 support in a bail hostel in north London. Aged 33, he told me: “They have made me tired, like an old man.”

The argument that policy has toughened up because of political pressure seems an obvious conclusion to draw. It is also backed up by a case currently before the Supreme Court, known as WL.

WL is a Congolese national who was part of a group claim for unlawful detention in 2008.

While the court was deciding whether or not he had been detained too long, the Home Office disclosed that they had been referring to a secret policy when detaining foreign prisoners at the end of a sentence.  While the published policy stated that there should be a presumption of release, this secret policy stressed a presumption of detention.

The judge decided that having a secret policy was unlawful, but lawyers and the Home Office are now arguing over whether an unlawful policy creates unlawful detention.

The Home Office say they would have detained WL anyway, even without reference to the secret policy. Lawyers say this argument is a nonsense.

For a layperson, like myself, it’s a complex case to follow, but it’s an important one.

The court is also examining the wider argument about what powers the Home Office should have to detain foreign prisoners when they are trying to remove them. The judges sat in November and a result is due sometime soon.

Meanwhile, WL has decided to return to the Congo.  After almost five years in immigration detention he couldn’t fight anymore. His lawyers will continue to fight on his behalf.

Whatever the court decides, politicians are still key in deciding what limits there should be on the power to detain for immigration purposes.

The UK is one of only a few countries to have opted out of the EU Removals Directive, that set a limit on immigration detention of 18 months. In reality, the UNHCR told me, most countries detain for far shorter periods than that.

Simon Hughes has campaigned against indefinite detention, but when I met him, he insisted that it’s not a result of policy decisions, just administrative failure. He disagrees with the idea that there should be a time limit on detention. He argues that public policy overrides human rights when it comes to non- UK citizens who commit crimes.

‘Citizenship is conditional’ he stressed, and told me that politicians of all stripes will not back a change to that approach.

The use of detention to control migration is on the increase, here and across Europe. When I spoke to Keith Vaz, head of the Home Affairs select committee, he told me that the real aim should be to ensure people don’t even make it to Europe.

Tougher, tighter controls are the future and it’s a future that is being shaped by politicians right now.

You can hear the interviews with Simon Hughes, Keith Vaz and the lawyers and ex detainees I spoke to on the Guardian website (click here).

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