About 18 months ago, in the lockdown summer of 2020, I started to argue that the Government's response to Covid is driven not so much by medical science or epidemiology, but instead by the psychological insights of behavioural scientists. Controversial "nudge theory" lies at the heart of Westminster's response. It refers to sneaky attempts to prime, prepare and prod us into their desired mindset and course of action, without us ever realising we are being coerced. Once nudge is seen, it can't be unseen. This week, the Government may have overplayed its hand. On Tuesday, Professor Neil Ferguson, the Imperial College epidemiologist whose modelling was used as the basis for the UK's lockdown policy, made an illuminating comment on BBC Radio 4's Today programme. "Nobody likes having their freedoms curtailed by measures but it's prudent to be cautious," he told presenter Sarah Smith, "and wearing masks certainly helps that: it reminds people we're not completely out of the woods yet." It was a startling admission, if we needed one, that masks are as much about psychology as they are about preventing infection. They act as a social cue, to use the language of behavioural scientists, nudging us into vigilance. These psychological cues are carefully calibrated, more so than many realise. In a document drawn up by the "Nudge Unit" ... scientists examine the success of Slovakia's mass testing programme, looking at how we could replicate that success in the UK.