The UK government has decided to fully reopen schools as soon as September!
That's right! Every child in the UK, plus a number of adults, will be attending a compulsory indoor mass gathering of several hundred, usualy several thousand people 5 times per week lasting 6+ hours each time. All this after WHO made it very clear that COVID-19 spreads much more easily indoors!
Therefore, there is no logical explanation that could be given to cancel London at this point as it is a one-time outdoor gathering lasting less than 5 hours for most people.