London is at a “critical time” in fighting Covid-19, a world health chief warned today as figures showed the number of new cases edging up in two thirds of boroughs.

Dr David Nabarro, the World Health Organisation’s coronavirus envoy for Europe, stressed that the risk of a surge in Covid infections in the capital was now “extremely serious”.

Speaking to the Evening Standard, he appealed to millions of Londoners not to “bend the rules” on social distancing and good hygiene with another heatwave on the way. He also emphasised that the “toughest time” to control the virus is when numbers are low because people often struggle to maintain discipline in combating it.

Dr Nabarro issued the warnings as figures showed the number of confirmed new cases and infection rate going up slightly in 22 borough areas.

Hackney and City of London saw 59 new cases in the seven days to July 30, a rate of 20.5 per 100,000, compared with 43 the previous week and a rate of 14.9. Barking and Dagenham saw its number of new cases nearly treble from 11 to 29, with the rate up from 5.2 to 13.7.

Barnet, Brent, Kensington and Chelsea, as well as Hammersmith and Fulham, all saw their rates go up to at least seven, with the number of new cases in the week to July 30 being between 30 (Barnet) and 11 (K&C), according to the analysis by Press Association of Public Health England figures.

Other boroughs with new cases nudging up, often from a low base, include Harrow, Lambeth, Westminster where the number of new cases doubled from eight to 17, Redbridge, Hounslow, Lewisham, Newham, Wandsworth, Greenwich, Enfield, Richmond, Hillingdon, Camden, Croydon, Waltham Forest and Bromley.