The Government's public health service has issued a heatwave warning as temperatures creep towards the 30 degrees Celsius mark in London and Surrey this week.

Public Health England's Level 2 Health warning is triggered when the Met Office forecasts that conditions will remain hot for long enough to be potentially harmful.

The heatwave period is expected to start on Thursday evening and go into Friday daytime and through until Saturday daytime.

Temperatures reached 26 degrees in parts of southwest London today and are forecast to reach 29C on Friday. 

Dr Paul Cosford, director for health protection at Public Health England (PHE), said: "While many people enjoy hot weather, high temperatures can be dangerous, especially for people who may be particularly vulnerable such as older people, young children and those with serious illnesses."

He added: "To prepare for any type of hot weather this summer, we strongly encourage each locality to consider the actions in this plan and adapt them to their local situation, as a component of wider resilience planning and long-term climate change adaptation arrangements.

"Everyone can enjoy the sun safely by keeping out of the heat at the hottest time of the day, avoiding sunburn and staying hydrated with plenty of cool drinks.

"Older people and those with long-term illnesses are particularly vulnerable to the effects of very hot weather, so it’s important to look out for them and keep indoor areas as cool as possible."

Steve Ramsdale, deputy chief meteorologist at the Met Office, said: "We’ve got hot and humid air moving up from the continent which will see temperatures rise through to the weekend, with some high day and night-time temperatures expected by Friday.

"The humidity will make it feel close, muggy and uncomfortable for many in the heat and people should take steps to keep cool – particularly across the areas where we have issued a heat health alert.

During hot spells vulnerable groups, such as the older people, feel the acute effects of heat more than others and it’s long been recognised that death rates rise in the early stages of heatwaves."

Many members of the Muslim community may be fasting during the current period of Ramadan. The NHS and the Muslim Council of Britain has published information for those affected.

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PHE's top advice for being sun safe:

  • try to keep out of the sun between 11am to 3pm;
  • apply sunscreen of at least SPF15 with UVA protection;
  • wear UV sunglasses, preferably wraparound, to reduce UV exposure to the eyes;
  • wear light, loose-fitting cotton clothes, a hat and light scarf;
  • drink lots of cool drinks;
  • look out for others especially vulnerable groups such as older people, young children and babies and those with serious illnesses;
  • never leave anyone in a closed, parked vehicle, especially infants, young children or animals