They have some influence as a show of strength by people holding common beliefs, such as the gigantic marches in London by Remainers opposed to Brexit between 2016 and 2019. These marches showed that there were millions of people who wanted the UK to stay in the EU, but we knew that already from the outcome of the referendum.

At the end of the day, all those marches and the organisation that went into it had little positive effect. In my experience, marches that go off without incident are boring to participate in, boring to watch and boring for the media, so they get limited news coverage.

Yet protest marches and demonstrations are one of the propulsion units of history, destroying governments and bringing down regimes that believed they had a firm grip on power. The common feature in the protesters’ success is that they provoke, intentionally or unintentionally, a violent overreaction by the authorities. The most striking example of this in the UK was the civil rights march in Derry in Northern Ireland on 5 October 1968, which was attacked by the Protestant-dominated police in front of the television cameras and thus began the unravelling of the Northern Ireland state.

The lesson from this should have been fairly obvious, but in 1972 the authorities had the imbecilic idea of policing an anti-internment march, again in Derry, with paratroopers who shot dead 13 civilians on Bloody Sunday and permanently delegitimised the British state in the eyes of the Catholic population.

I have always been mystified by why governments overreact, using violence against peaceful protesters that do not seriously threaten them, when it is so obviously in their interests not to do so. Two contradictory motives are usually at work. One is an underestimation of the protesters as an atypical minority who can be safely quashed without the wider community objecting. The other – and authoritarian regimes are particularly prone to this – is an overestimation of the danger posed to the leadership by mass protests on the streets, which they try to suppress with extreme violence

I witnessed a grotesque example of overreaction by the security forces generating just such a powerful protest movement in Baghdad in October 2019. I had talked to the organisers of some scantily attended protests demanding jobs and opposing government corruption who were gloomy about their prospects of achieving anything. But as I sat in my hotel room near the protest site in the city centre, I heard the pop-pop of gunfire that turned out to be the security forces opening fire on a peaceful crowd and killing 18 people. Within days, protests were convulsing the whole of Iraq.

Sometimes repression succeeds and the government kills or frightens enough people to drive them off the streets, as the army is trying to do in Myanmar. But once a government goes down this road, there is no retreat and its very existence is in play.

In Britain there have always been effective mechanisms for reducing the political temperature and deflating criticism of the government through prestigious inquiries and mass protests, neither of which achieve very much.

The Boris Johnson government may regret devaluing these well-established instruments of control. If the new law on protests is enforced, it will spark frequent confrontations between protesters and the police. If it is not, then the government will feel that it is being challenged and made to look weak, provoking a self-destructive overreaction.