How long will the London heatwave last? Extreme heat warning as temperatures to hit 40C

Temperatures in London could hit 40C in the second heatwave of the year as a red warning for extreme heat is issued.

The heatwave follows a record-breaking May, when the UK recorded its hottest ever day for the month at 35.1C.

To add insult to injury, the high humidity is expected to make the heatwave feel especially uncomfortable.

Londoners should also brace themselves for a record four tropical nights from Tuesday to Friday with the temperature never dropping below 20C.

There will finally be some respite at the weekend, with temperatures set to fall to 27C by Sunday according to the Met Office.

While London is partial to some sunshine, the majority will be glad to see the end of the five-day heatwave which brings with it sleepless nights, sweaty commutes and unbearable working conditions.

A heatwave is officially defined by the Met Office as a period of at least three days when the temperature stays above a certain threshold. In London, this threshold is 28C.

The heat warning flags potential health impacts for people vulnerable to extreme heat and heat-related issues for the wider population, as well as a potential increase in water safety incidents.

The red warning is in place from 9am on Wednesday to 9pm on Thursday, impacting London and much of the south-west and some of south-west Wales.

The Met Office is warning that the heat will be accompanied by high humidity, “exacerbating the potential for discomfort and health impacts.”

Dr Agostinho Sousa, head of extreme events and health protection at UKHSA, said: “Very hot weather is forecast across large parts of England in the coming days and we are urging health and social care services across the country to ensure they are prepared.

“It is vitally important that people understand the risk posed by high temperatures like these, and take steps to keep themselves and their friends, families and neighbours safe.

“Simple actions like staying hydrated, avoiding the sun during the hottest part of the day, and keeping your home cool can make a big difference.

“It’s also important to look out for others, especially elderly relatives, neighbours, and those with underlying health conditions, to make sure they are aware of the forecast and following the necessary advice.”