The case of the 15 activists convicted on Monday over a non-violent protest which stopped a deportation flight from leaving Stansted airport should not only worry all those who care about the rights of those threatened with removal. It should alarm anyone who cares about the right to protest. The disproportionate charge will have a chilling effect. Amnesty has called this “a crushing blow for human rights in the UK”; Liberty said it was a “malicious attack” on the right to protest.

There is no dispute that the members of the End Deportation group cut through a fence and secured themselves around a plane chartered to remove undocumented immigrants to Nigeria, Ghana and Sierra Leone. The question was whether their reasons for doing so constituted a defence (the judge said not), and whether the charge was appropriate. The first issue is a matter of law. The second is also one of common sense. They were initially accused of aggravated trespass, the offence used in previous airport protest cases. The Crown Prosecution Service then upgraded this to “intentional disruption of services at an aerodrome” by means of “a device, substance or weapon”.

This obscure-sounding charge was introduced in response to the Lockerbie bombing and carries a correspondingly harsh maximum penalty: life imprisonment. It has been used just once before, 17 years ago, in the case of a pilot who deliberately flew his helicopter at Coventry airport’s control tower.

The CPS maintains that the group “placed themselves, the flight crew, airport personnel and police at serious risk of injury or even death”. Devices in this instance meant not explosives but “industrial bolt cutters, chains, expanding foam, scaffolding poles and lock box devices”. The prosecution also argued that the protesters created a kind of secondary endangerment; by diverting police attention, it made other parts of Stansted more vulnerable to any potential terrorist attack.

The protesters were highlighting a harsh and punitive system with which many are rightly and increasingly ill at ease. In June this year, Virgin airlines said it would no longer help deportations. Relying on charter flights (in several cases from an RAF base, following the Stansted protest) only veils the issue. Nearly half of immigration decisions are overturned on appeal; the Home Office loses 75% of its appeals against immigration rulings. Two people on the Stansted flight have been saved from wrongful deportation, having now been granted the right to remain; nine more remain in this country while their cases are considered. The best response to such protests would be to overhaul the cruel immigration regime, ensuring a fair and humane system.

These charges were a grave mistake. The attorney general should never have approved them. Attention now turns to the dangers of heavy sentences. These would compound the unfairness. But the underlying injustice should be fully resolved on appeal.