I very much hope they're just being enormously over-cautious with Boris. The imperial study = someone of his age has a 10% chance of reaching hospital. From there, only 12.2% chance of requiring 'critical care' (ie, 1.2% of all infections). 0.6% of all infections do not make it.

Not amazing odds, hence hoping they are being ultra ultra cautious & he wouldn't ordinarily be in that 12.2% bracket.