SUNBATHERS have been warned against “overdoing it” while enjoying temperatures of up to 34C (93.2F) this week with very high UV levels expected.

Temperatures in Brighton could reach at least 26C on Friday, hotter than Portugal, Jamaica, Costa Rica, the Canary Islands and Cyprus.

These areas may see an official heatwave between Wednesday and Saturday, which is when at least three consecutive days have daily maximum temperatures meeting or exceeding the heatwave temperature threshold. The threshold varies by county.

People looking to top up their tans, swim in open water or use public transport have been warned to be wary.

Craig Snell, a Met Office forecaster, said: “Very high UV levels are expected in the south this week, meaning people should really avoid being in the sun during the midday hours.

“Wearing sunglasses, a shirt, a hat and sunscreen are essential to protect the eyes and skin, and drinking lots of water is important – long exposure to the sun can be dangerous.

“People should avoid overdoing it. We all love the sunny weather, but being sensible can help you avoid a nasty sunburn.”

Friday is predicted to be the hottest day of the year so far, eclipsing the 27.5C set in mid-May at Heathrow.

It could also be the hottest June day for the UK since records began if temperatures top the 35.6C recorded in Southampton in 1976.

The threshold for a heatwave is 25C for Wales, Scotland and south-west England, 27C for southern and eastern England, and 28C for London.

People have been told to expect “uncomfortable” nights when trying to sleep, with temperatures remaining in the low 20s in the evening.

Those with hayfever have been advised to be wary of very high pollen levels.

Here is the forecast for Brighton

Wednesday: Dry with light winds and prolonged sunshine through the day. Becoming very warm or hot inland, though fresher again at the coast where sea breezes may develop from late morning. Maximum temperature 28 °C.

Outlook for Thursday to Saturday: Dry and sunny Thursday. Similar Friday though a risk of showers later. Probably cloudier Saturday with a chance of rain or thunderstorms. Very warm or hot, perhaps very hot Friday.