A Level 3 Government heat health warning has been issued, one behind a national emergency, with temperatures reaching 28C in Sheffield.
The Met Office has confirmed that today is the hottest day of the year, however temperatures are expected to rise this week.
The Level 3 warning was issued this morning and will last until Wednesday morning with temperatures expected to reach up to 35C in some parts of the country.
The notice orders hospitals to be on guard with health staff also needed to make daily contact with the ill, vulnerable and elderly.
Dr Thomas Waite from Public Health England said: "Much of the advice on beating the heat is common sense and for most people there’s nothing to really worry about.
"But before the hot weather arrives, it is a really good time to think about what you can do to protect you and your family and friends.
"For some people, such as older people, those with underlying health conditions and those with young children, the summer heat can bring real health risks.
"That’s why we’re urging everyone to keep an eye on those you know who may be at risk this summer. If you’re able, ask if your friends, family or neighbours need any support."
Met Office Chief Meteorologist Frank Saunders said
"With high pressure building from the south west and warm air being drawn up from the Azores, much of England will see very warm or hot weather this weekend and into early next week.
"Daytime temperatures will widely be in the mid to high twenties with some central and southern parts reaching the low thirties. It will also feel warm and humid overnight."