More storm warnings have been issued across the UK on what is likely to become the hottest day of the year.

Forecasters say the mercury is expected to hit 33C in southern England but heavy showers and thunderstorms are set to batter a large swathe of the country.

A yellow warning issued by the Met Office spans east Wales, Yorkshire, Lincolnshire, Manchester, Nottingham and Oxford, and will be in place from 2pm to 9pm.

The same warning has been issued for Sunday covering Northern Ireland, northern parts of England and Wales as well as southern Scotland between 2pm and 11.59pm.

The UK has already sweltered through five days of temperatures above 30C in September for the first time, with that record likely to continue this weekend.

Thursday was provisionally the hottest day of the year, with 32.6C recorded in Wisley, Surrey.

Saturday, however, is expected to exceed that high temperature, with areas around London expected to bear the brunt of the hot weather.

The UK Health Security Agency has issued an amber heat health alert, meaning weather impacts are likely to be felt across the health service, with those aged above 65 or those with pre-existing respiratory or cardiovascular disease at greater risk.

Much of the UK will see high temperatures and sunny skies continue on Saturday, in what has a possibility of being the hottest day of the year so far

The Met’s yellow weather warning means some people could be in store for some flash flooding, lightning strikes, hail or strong winds, with possible interruptions to road access and public transport if such circumstances were to occur.

Met Office chief meteorologist Paul Gundersen said: “Although much of the UK will see high temperatures and sunny skies continue on Saturday, in what has a possibility of being the hottest day of the year so far, there’s also the potential for some thunderstorms, which has resulted in a yellow warning being issued for much of central England and parts of east Wales.

“Temperatures will begin to trend downwards from Saturday in the far north-west of Scotland, with a cold front gradually moving south through the weekend, bringing with it the risk of some heavy and thundery downpours on Sunday as well.

“However, the south-east will hold on to the high temperatures the longest and could still reach 32C on Sunday.”

Environment Agency flood duty manager Chris Wilding warned motorists against driving through floodwaters in the case of flash flooding.

Mr Wilding said: “Significant surface water flooding is possible but not expected across parts of England on Saturday afternoon and evening due to isolated intense downpours.

“We urge people not to drive through floodwater – it is often deeper than it looks and just 30cm of flowing water is enough to float your car.”

Mayor of London Sadiq Khan has issued a “high” air pollution alert for the capital for Saturday, the first since June, and urged Londoners to stop their engines idling and refrain from burning wood or garden waste.

But there is relief from the heat on the horizon, with the UK expected to return to cooler weather next week with a mix of sunshine, showers, and some windy conditions likely as temperatures return towards the average for the time of year.