New cases of coronavirus have more than doubled in the city in the space of a week.
Chancellor warns there is "always the risk" holidays may be disrupted, as virus cases climb in France.
Beachgoers are urged to avoid busy areas, as temperatures in parts of the UK reached 36.4C (97.52F).
The 13-year-old suffered suspected spinal and pelvic injuries after the "tombstoning" stunt.
The drop in office-based working has affected commuters in London's hospitality sector, experts say.