Andrew Mitchell is a former International Development Secretary, and is MP for Sutton Coldfield.

With Dostoyevsky’s maxim in my mind – that the degree of civilisation in a society is revealed by entering its prisons – I recently visited Brook House Immigration Removal Centre, near Gatwick. Prepared for the worst by the Panorama exposé and accounts of terrible conditions, I was pleasantly surprised. The regime seemed, to an outside observer, humane and decent, though clearly we must always ensure that individual behaviour by all staff is both transparent and accountable.

But neither the conditions for detention nor the debate as to whether or not G4S should run Brook House go to the heart of the matter. The best regime in the world cannot ameliorate the fundamental injustice of a system that arbitrarily imprisons people without time limit for solely administrative reasons.

This is not a matter of criminal justice, but of the administration of our immigration rules. The distinction is important. Many people in immigration removal centres have never been charged with any crime, while some have previously been in prison following conviction for a criminal offence but have served their time. All are detained purely and simply because they are liable for removal. Some go on to be removed, but more than half are, at an arbitrary later date, released and able to remain in the UK temporarily or permanently.

Recently, the most glaring abuse of this same immigration rule was the detention of English citizens who had come to the UK as children of the Windrush generation, an abuse of power which rightly generated a national outcry. The reality is that we remain the only country in Europe to detain people indefinitely for the purposes of immigration enforcement. So we need to ask ourselves whether the UK can reconcile the need to remove people without legal rights to remain in the country with a humane and just system of administration. In my opinion it can and it must.

If individuals have no right to remain here we should, in my view – as the key priority – strongly encourage other countries to accept the return of their citizens. Indeed, we should negotiate such deals and procedures as an urgent necessity. In this way individuals are no longer left in limbo in immigration detention. At the same time UK law must change if we want to be worthy of our oft-repeated claim to have the “finest justice system in the world”.

To end arbitrary unlimited immigration detention, I am proposing a simple change to our immigration law – the introduction of a 28-day time limit for administrative detention. Those people released from immigration detention without having leave to remain in the UK would be required to report to the police or the immigration service to offset any risk of absconding. They should, of course, be liable to further detention if they breached their reporting requirements. Already many people awaiting decisions from the Home Office comply with similar reporting requirements.

My modest proposal only applies to the use of arbitrary indefinite administrative detention. Convicted criminals will serve their sentences, and will then face removal if they have no right to remain. If the crime is particularly serious and the prisoner presents a risk to public safety, it will be for a criminal parole board to carry out a risk assessment and to decide when and if an individual can be released. In those extreme cases, we should surely expect the immigration service to have removal arrangements in place to coincide with the release date.

I am not proposing a seismic change, but one that will nevertheless save the country over £500 a week per person currently spent on detention. This is a significant saving since 27,331 people entered detention in 2017. In addition, I was surprised to discover that over the past five years £21 million has been paid out in damages for unlawful detention. This figure, revealed in response to a question I asked the Home Secretary recently, could be vastly reduced – if not eradicated – if a 28-day time limit were in place.

The absence of a time limit does nothing to promote speed and efficiency in the administration of justice by the immigration service. I hope that the introduction of one will improve working practices as well as creating a more humane system of immigration control.