The warning comes as the Met Office forecasts increasingly hot and humid conditions across London and south-east England, with some areas potentially meeting official heatwave criteria by the weekend
A yellow heat health alert has been issued for London as forecasters warn temperatures could climb to 30C later this week.
The UK Health Security Agency (UKHSA) has placed the capital under the alert from 3pm on Wednesday until 8pm on Monday, June 22, amid concerns that rising temperatures could impact vulnerable people and put pressure on health services.
The warning comes as the Met Office forecasts increasingly hot and humid conditions across London and south-east England, with some areas potentially meeting official heatwave criteria by the weekend.
Meteorologists say Friday is likely to bring the hottest weather, with temperatures in parts of London potentially reaching around 30C.
However, forecasters have warned it will not be continuous sunshine, with cloud cover expected at times and the possibility of thunderstorms.
Met Office meteorologist Jonathan Vautrey said temperatures are expected to rise steadily through the week, while humidity levels will also increase.
He warned Londoners are likely to notice increasingly muggy conditions during the second half of the weekend, with uncomfortable nights expected as overnight temperatures remain in the high teens.
According to the UKHSA, yellow heat health alerts indicate there could be minor impacts across health and social care services, particularly affecting older people and those with underlying health conditions.
The agency also warned of an increased risk of indoor spaces becoming dangerously warm and a higher likelihood of water-related incidents, including cold water shock and drowning.
Londoners are being advised to stay hydrated, avoid prolonged periods in direct sunlight during the hottest parts of the day, and check in on vulnerable relatives and neighbours as temperatures rise.
