By the way, the reason I thought end of May was because of this 'review after three weeks' suggestion. I thought after one set of three, people would accept a further period, after two they would be some grumbling, and after three lots of three weeks the grumbling would be loud enough in some quarters that a slight relaxation of the lockdown became likely. So nothing to do with scientific justification, but largely based on my impression of how some people will react to being locked down. And interesting had it been a 4 week period or a five week period, I think it would still be the third review that would be a problem: it is the reviews not the length that determines the dates.