Temperatures are forecast to climb into the 30s this week as the UK braces for days of scorching weather.
The Met Office has issued a four-day amber warning for extreme heat in parts of England and Wales for Thursday to Sunday, with temperatures expected to hit 36C in some areas.
A heat health alert is also in place from the the UK Health Security Agency (UKHSA) as experts warn the hot weather is likely to cause adverse health effects, particularly among the elderly, young children, and those with existing health conditions.
It comes as months of low rainfall and hot spells have left parts of the UK facing drought, prompting hosepipe bans and warnings on the impact on agriculture, rivers and wildlife.
Thames Water has had to supply bottled water for residents of the village of Northend in Oxfordshire and pump water into the network after supplies were disrupted.
Three other water companies – South East, Southern and Welsh Water – have announced hosepipe bans for customers in areas they supply.
Elsewhere, grass fires have broken out as the heat and lack of rain have left countryside, parks and gardens tinder-dry, prompting calls for people not to have barbecues and for disposable barbecues to be banned.
Temperatures are not set to be as extreme as those in July which smashed records when the thermometer climbed to above 40C for the first time,but the UKHSA is urging people to take care in the heat and be aware of the common signs of heat exhaustion and heatstroke.
Heat exhaustion is not usually serious if you can cool down within 30 minutes, but if it turns into heatstroke, it needs to be treated as an emergency, the NHS says.
If you are out enjoying the warm weather this week, these are the key symptoms of heatstroke to be aware of, and when you should seek medical help.
1. Headache
Headaches are not usually a sign of something serious, but can occur after spending too much time in the sun. Drinking lots of water should help to ease symptoms and taking paracetamol or ibuprofen.
2. Dizziness and confusion
Dizziness includes feeling off-balance, lightheaded or faint, or feeling like you or things around you are spinning. It is a common symptom of dehydration and heat exhaustion, and can be treated by drinking plenty of water, rest and lying down until it passes.
3. Loss of appetite and feeling sick
If you lose your appetite or feel nauseous after spending time in the sun, it could be a sign you have heatstroke. Taking regular sips of a cold drink can help with symptoms, as well as ginger or peppermint tea, or foods containing ginger.
4. Excessive sweating
If you experience excessive sweating and have pale, clammy skin, you may be suffering from heatstroke. Taking cool baths or showers, sprinkling cold water over your skin or clothes, and wearing light-coloured, loose clothing should help with symptoms.