Eleven years ago, Labour home secretary John Reid admitted that the Home Office's immigration systems were "not fit for purpose". The problems were extensive. "It's inadequate in terms of its scope, it's inadequate in terms of its information technology, leadership, management systems and processes," he concluded.

Over a decade later, nothing has changed. It is a catastrophic department – misleading the public, ransacking the lives of those it deals with and proving utterly ineffective even on its own terms. It is hard to see where the malice ends and the incompetence begins, but you get a sense that perhaps both qualities interact with each other. Maybe the ineptitude it displays is itself a form of malice, or at least evidence of it.

This week the Office of National Statistics (ONS) admitted that far fewer international students overstay their visa than previously estimated. The Home Office had claimed it was 100,000. The real number was 4,600. Some 96.3% of them depart in time .

There is good reason to think the Home Office knew about this. Back in October last year, the Times reported that a secret government study had found very low levels of students overstaying their visa. But the findings threatened to undermine Theresa May's mission to keep student numbers in the official immigration figures. So the report was kept secret and not shared with other departments or the press.

While these figures were kept under wraps, the Home Office was still pursuing its mass student deportation programme in the courts, targeting tens of thousands of them on hearsay evidence, detaining them and removing them, often without trial.

The row over the student figures came as Dr Eva Johanna Holmberg, a Finnish academic working in Britain, received a letter from the Home Office demanding she leave the country immediately.

By the end of the week the Home Office had apologised and said that the letter, together with 100 others, was an error. The same process took place last year, when European citizens started receiving letters saying they should pack their bags. Except this time the letter is more severe, constituting a formal order for expulsion. They either do not care enough to prevent these errors, or there is something darker going on. The malice and incompetence the department exhibits makes it hard to conclude one way or the other.

Meanwhile, new details were emerging of a programme by which victims and witnesses of crimes have their information passed on to the Home Office for immigration enforcement. This type of thing is happening at all levels. Data collected by charities supposedly helping rough sleepers was used to deport them. Now sex workers are finding that they are being threatened with deportation after reporting a crime against them to the police.

Again, the policy is ineffective and dangerous. It discourages people from going to the police when they have been the victims of crime. It makes it harder for the police to solve crime because witnesses will be afraid to contact them. But on it goes, with cross-party support, including from the London mayor.

While these stories garnered some decent media attention, very few people noticed the new statistics on detention centres published this week. Hardly anyone ever does. We don't like to speak about our dirty little secret, where we lock people up without trial for unspecified periods.

In the year to June 30th, 2017, 27,821 people entered immigration detention in the UK. Over half of those detained at the cut-off date had been in detention for more than 28 days. Eighty people had been detained for over 12 months, one man for more than four years.

Dig into the data and the true pointlessness of the policy becomes clear. Detention is supposed to be a last-resort measure to facilitate removal from the country. But over half the people detained (52%) in the quarter ending June 30th 2017 were released back into the community. Even on its own terms, the detention system is a failure. And that is not to count the vast waves of taxpayer cash directed towards it or the trauma of the people who are taken away in front of their family or co-workers and locked up, with no idea of when they will be released.

Wherever you look, the Home Office is failing. Perhaps this is all cock-up rather than conspiracy. That's usually the right interpretation. But there comes a point – a cock-up threshold, if you like – where it becomes a form of conspiracy in itself. Even if this is all a result of simple incompetence, it is an incompetence which is tolerated and which has been left unaddressed for well over a decade. Perhaps they tolerate it simply because they don't care about those they have jurisdiction over. Or perhaps they tolerate it because the Kafkaesque horror story of our immigration system acts as a deterrent towards those who wish to live here.

Ian Dunt is the editor of Politics.co.uk. His book – Brexit: What The Hell Happens Now? – is available now.

The opinions in politics.co.uk's Comment and Analysis section are those of the author and are no reflection of the views of the website or its owners.