As therapies go, lockdown was ­devastating. In our preliminary discussions about these types of intervention – telling people not to go near each other – we had all assumed that we would have a problem ­persuading them to comply.

Chief Medical Officer Chris Whitty, scientist Patrick Vallance and I had thought that if some Tory PM appeared on TV and told the British people not to go to the pub, and then not even to venture out of doors, their natural cussedness and libertarianism would encourage them to stick two ­fingers up to government.

Well, as it turned out, lockdown was an easy sell, and indeed my stay-at-home message was heeded so punctiliously by the workforce that the UK sustained the biggest fall in output since the Great Frost of 1709. The trains were empty. Town centres were silent. The streets were deserted save for the cats – which we first believed, probably wrongly, not to be vectors of the disease.

In that terrible April in 2020, new car sales fell by 97 per cent – not surprisingly, since I had shut the showrooms. National compliance was so total that we even desisted from some types of economic activity that were theoretically intended to continue – such as construction – and which did in fact continue in countries such as France and Germany.

With the traffic off the streets and the trains deserted, this could have been the ideal moment to accelerate that infrastructure roll-out: use Covid-secure protocols to build those bypasses, upgrade that track, send the fibre-optic cable sprouting through the national wainscot.

We missed that chance, Crossrail was delayed, HS2 ground to a halt, and as the cost of it all exploded I felt as if the vast crenellated sandcastle of my plans was being washed away by the tide of the virus. Around April 20, it started to look as though we had been through the crest of the wave. We had gone up more than 1,000 deaths per day, but now the totals were falling – both for deaths and hospital admissions.

They were still horrendous – 800, 700, 600 – but the trajectory was clear. It looked and felt to me as if the great national effort was beginning to work. All that privation, all that seclusion – it was starting to deprive the virus of targets; we were protecting the NHS and ­saving lives.

At that moment I believed in the correlation between the non-pharmaceutical interventions – the lockdown and other restrictions on human contact – and the shape of the epi curve. I believed that we had bent that parabola by the strength of our collective will, like Uri Geller with a spoon.

It was only later that I started to look at the curves of the pandemic around the world – the double hump that seemed to rise and fall irrespective of the approaches taken by governments. There were always two waves, whether you were in China, where lockdowns were ruthlessly enforced, or in Sweden, where they took a more voluntary approach.

Looking back, I wonder if King Cnut was right all along when he stationed his throne on the shore of the Thames and asked his courtiers to watch as he vainly ordered the tide to withdraw. Maybe there are limits to human agency; maybe it isn’t possible for government action to repel the waves of a highly contagious disease, any more than it is possible to repel the tide of the Thames.

I am not saying that lockdowns achieved nothing; I am sure they had some effect. But were they decisive in beating back the ­disease, turning that wave down? All I can say is that I am no longer sure.

Adapted from Unleashed by Boris Johnson (William Collins, £30), to be published on October 10. © Boris Johnson 2024. To order a copy for £25.50 (offer valid until October 12, 2024; UK P&P free on orders over £25) go to mailshop.co.uk/books or call 020 3176 2937.

Boris Johnson will be in conversation with Gyles Brandreth at The Bridgewater Hall, Manchester, on October 12.