As today’s devastating exposé in the Guardian makes clear, something has gone fundamentally wrong with the Home Office’s treatment of skilled migrants.

Under an obscure clause of the immigration rules as currently applied, if migrants who have been granted indefinite leave to remain make mistakes in their tax returns that are judged by the Home Office to have been deliberate, they are ruled to be guilty of such a serious offence that they become non-persons – nominally “illegal immigrants”.

They are deprived not only of leave to remain, but of the most basic human rights: to earn a living, buy or rent property, or receive medical treatment if they are ill. They also become liable to deportation at short notice to their native country, with which most no longer have any ties. The punishment is wholly disproportionate to the nature of the crime.

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The trial of this alleged offence, being a matter delegated to the Home Office, is not conducted by an independent judge and jury but by civil servants responsible to their boss, the home secretary, whose government’s policy is to reduce the number of immigrants and maximise the number of deportations.

Deciding whether an error in a tax return is deliberate or unintended is not a simple matter. The Home Office’s official advice to skilled migrants is to employ a qualified accountant to help them with their tax return because of its importance. Yet the Home Office teams investigating a mistake more often than not ignore the fact that the tax return was made on an accountant’s advice. In their view, the taxpayer is personally responsible.

Furthermore, HMRC are experts, trained to detect deliberate fraud. If fraud is proved, they will impose financial penalties. Yet in many of the cases of migrants accused of cheating, Home Office investigators, who are not tax experts, ignore the fact that HMRC has imposed no penalty because they did not find the error to be deliberate.

Another flaw in the procedure is that the test now required under rule 322 (5) is whether a person’s character and conduct are such as to make them undesirable residents. Yet in many cases no inquiries have been made about either. To complete the catalogue of injustice, in most cases there is no right of appeal; and even when there is, the accused is denied legal aid. When a right of appeal does exist, a majority of appeals are successful.

This denial of basic rules of justice would never be tolerated if generally known. There should always be a right of appeal, with compensation where appropriate, and the right to legal aid. There should also be independent representation on the investigating team, as is common in cases of professional misconduct.

Above all, the Home Office should recognise that rule 322 (5), the rule leading to these multiple injustices, is wholly unfit for the purpose.

• Dick Taverne is a Liberal Democrat peer