It's not just London that has had its calendars blocked, @Gilla4 - Calendars have been blocked in the whole of the UK. - Check your inbox for your regular email; we UK hosts were sent info there; at the time of the original block on 23 March, and for every extension since.
I guess this is because it is still illegal, against Covid-19 emergency legislation, for ANYONE to travel for non-essential purposes, and illegal for any / all accommodation providers to let rooms/units.
Our government has said that holiday accommodation will be able to reopen on 4 July ONLY IF the coronavirus is sufficiently under control. (R number <1)
Having said that, there are those of us who are puzzled by the block, because it still IS legal to accommodate certain types of WORKERS, working away from home.
Some of us would like to be trusted to make the decision, only to host those whom we can legally host, and to decline bookings from people having a break/holiday, or visiting friends/family, which is still against the emergency laws.
I guess Airbnb does not trust us all to act within the law. (Maybe because SOME hosts hosted illegally at the beginning of lockdown.)