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Simon King
BBC weather presenter and meteorologist

While the heat builds today in England and Wales, for Scotland and Northern Ireland the peak of this warm spell was Wednesday.

The highest temperatures were 24.4C (76F) in Scotland (Aboyne) and 24.1C in Northern Ireland (Castlederg).

All change today though.

With a cold front moving south-eastward, there’s more cloud with some showery outbreaks of rain and cooler air behind it.

Temperatures will be 8 to 11 degrees lower than on Wednesday, with 12C in north-east Scotland and 14 to 18C more widely elsewhere - closer to the average for early May.

Francesca Gillett
Live reporter

Not that I’m feeling envious, but I’ve just compared the temperatures we’re having in Sydney at the moment to London where I usually live.

The centre of the city peaked at 18.2C (64.8F) on Wednesday and is similar today.

We also had 17mm (0.6 inches) of rain yesterday and another 14mm into this morning.

Don’t feel too sorry for us though... it is autumn down under and we’re forecast to have a few sunny days next week!

While for many the warmer weather is generally a welcome change after months of dreary winter, it can be a bit of a nuisance and pose some health risks for others.

Here are some reminders and pointers on how to stay cool and safe:

• Make sure you’re drinking enough water and eat foods with a high water content, such as watermelon and cucumbers, to avoid dehydration
• Wear loose-fitting clothing and breathable fabrics, such as cotton, linen and moisture-wicking synthetics
• Opt for a hat and sunglasses for extra protection and to avoid direct sunlight
• Stay in the shade - the NHS recommends avoiding the sun between 11:00 to 15:00 BST, generally the hottest part of the day
• Use fans, ice and cool showers to reduce your body temperature
• Close your windows during the day and open them at night when the temperature drops

Image source, PA Media

The London Fire Brigade has urged people to stay safe after a rise in water-related incidents.

Last year, its crews responded 565 times. So far this year, its boats have been deployed to more than 70 incidents already.

Assistant Commissioner Patrick Goulbourne warns that "even when the sun is shining, water temperatures can be dangerously cold".

He says: "Cold water shock can affect anyone, regardless of fitness or swimming ability. It can lead to water inhalation and, in the worst cases, drowning."

Earlier this month, the Metropolitan Police warned of the dangers of swimming in rivers and lakes after the deaths of two children in London.

The RNLI is also urging people to choose a lifeguarded beach where possible, and to swim between red and yellow flags.

If you get into trouble, the advice is to Float to Live, external - and if you see someone struggling, call 999 and ask for the Coastguard.

Simon King
BBC weather presenter and meteorologist

While Wednesday was the warmest day of the year - with a maximum temperature of 26.7C (80F) recorded in Wisley, Surrey - Thursday is set to be even warmer across England and Wales.

Temperatures will climb quickly through the morning, reaching 24 to 29C this afternoon.

This would make it the warmest start to May on record, exceeding the previous record of 27.4C set in Lossiemouth in 1990.

While there is a small chance, I wouldn’t be surprised if we even perhaps nudge into 30C in the London area later today.

That’s significant because it would be the earliest date in the year the UK has recorded 30C since records began in 1860.

Adam Durbin
Live editor

For the last few weeks most of us have been able to enjoy the spring sunshine.

Well, it is about to get even warmer - and today we could see the hottest May Day on record.

Temperatures here in London could reach a sweltering 29C, while other parts of the UK are also expected to bask in the warm - though not all.

We have one eye this morning on the rail and London Underground networks to tell you if there are any heat-related problems, while our colleagues at BBC Weather will be bringing the most up-to-date forecasts.

For those heading outdoors, remember your suncream, breathable clothing and to embrace the shade during the hottest part of the day - plus we'll have some more tips on how to cope with the heat.