Worth a read, and I’m not just saying that because I’m quoted:

Britain is the only European country to allow indefinite detention under immigration laws. Some of those held are migrants who have committed crimes but cannot be removed, because their home countries are too dangerous. But of those detained last year, more than two-fifths ended up being released. This suggests poor decision-making about who is detained in the first place, says Colin Yeo, an immigration lawyer…

In recent years Britain’s government has shifted its focus to trying to persuade unauthorised immigrants to leave of their own accord. In 2013 Mrs May, then the home secretary, put up posters and sent vans around British cities emblazoned with: “In the UK illegally? Go home or face arrest”. The next year it became government policy to create a “hostile environment”, by denying unauthorised immigrants bank accounts and driving licences, making it harder for them to get health care and fining landlords who did not check their tenants’ immigration status. In 2016 forced returns of migrants fell by 15% compared with 2014; those of failed asylum-seekers fell by 53%.

But there is little evidence that hostile-environment policies do anything except encourage illegal immigrants to steer clear of the authorities: the posters and vans were abandoned after being deemed a failure. Meanwhile, the attempt to squeeze net immigration down means applications to enter or settle in Britain seem to be denied whenever possible, rather than being decided on their merits.

Source: Exit strategies: Removing unauthorised immigrants is difficult and expensive | The Economist