Hot temperatures forecast to hit scorching 31C peaks in parts of the UK this week amid a short-lived heatwave have sparked health concerns for older people more vulnerable to heat-related illness.

Monday was the hottest day of the year so far, reaching 28.3C in Wisley, Surrey, and temperatures are expected to rise even higher in parts of central and eastern England on Wednesday, the Met Office said.

The UK Health Security Agency (UKHSA) has issued yellow heat health alerts across most of England.

They will remain in place until Thursday, when forecasters expect temperatures will begin to return to their seasonal averages.

Andrea Bishop, a Met Office spokeswoman, said it will continue to be “very warm” across much of the country over the next few days, though conditions in the west and the South West will be “nearer average temperatures”.

“Wednesday is a very warm day for many and we’re going to have top temperatures of 31C,” she said.

“We then transition to fresher conditions looking very likely through Thursday as a weakening band of cloud and showery rain runs east, south-east, across the country through the day.

“Although it could still be very warm ahead of this, for example in the east or south east of England.”

Heat exhaustion, heatstroke and dehydration are the main risks posed by heatwaves and hot weather.

NHS guidance says older people, especially those over 75 and female, are most vulnerable to heat-related illness, as well as people with serious or long-term illnesses, and very young children.

Age UK recommends older people take particular care not to spend too much time outside during the hottest part of the day – between 11am and 3pm – and keep the blinds down and windows closed to remain cool inside.

Dr Luke Powles, associate clinical director at Bupa Health Clinics, said it was important to know the symptoms of heat exhaustion, which include “a throbbing headache, dizziness, confusion, cramping and nausea” and heatstroke, which is much more serious.

“The symptoms of heatstroke include not sweating even while feeling too hot, a high temperature of 40C or above, fast breathing or shortness of breath, feeling confused, loss of consciousness and being unresponsive,” he added.

“Heatstroke is very serious and should be treated as an emergency.”

Drinking lots of water is a crucial way to avoid heat exhaustion and dehydration, alongside keeping cool and staying in the shade.

Dr Powles said: “We should drink 1.5 to two litres of fluid a day, which is about eight to 10 glasses. However, if you’re in the heat during the day you can become dehydrated quicker, so drink more often and aim for at least two litres.”

Sunseekers heading to the beach to bask in the warm weather should use at least factor 30 sunscreen (SPF) in order to avoid sunburn, which can increase the risk of developing skin cancer, it is advised, even if it is cloudy.

Older people are more susceptible to heat-related health issues as their bodies are less able to cope with the rising temperatures.

During the record-breaking heatwaves of summer 2022, more than 2,800 excess deaths were recorded among over-65s.

Rob Martin, managing director of care services at Anchor, said the later living charity was urging “the wider community to keep a close eye on older neighbours and their older relatives who may live alone and are more vulnerable in the heat.”

“We recommend older people stay hydrated and keep out of the sunlight as much as possible,” he added.

“In these temperatures, it’s important to avoid caffeinated drinks as they are dehydrating. Drink plenty of cold fluids like water and fruit juices. We recommend taking regular sips of hydrating drinks throughout the day.”

Heatstroke also poses a risk to pets, especially dogs left unattended in warm cars or taken for walks on hot days.

The RSPCA recommends ensuring pets have access to shade and fresh drinking water to help them keep cool.

London saw a peak of 27.4C at St James’s Park on Monday, while temperatures rose to 26.9C in Aberdeenshire, Scotland, and 25C in Northern Ireland.

However, the heat is expected to last only until Wednesday with heavy showers, thunderstorms and persistent rain possibly returning in the west as the week goes on and cooler conditions are ushered in.