The UK has recorded its warmest day of the year so far, with temperatures hitting 29.4C, the Met Office has said.

However, the forecasting service said thunderstorms were “pushing into” the Channel, and an amber weather warning for severe thunderstorms in the east and south-east would come into force at 8pm on Friday.

A Met Office spokesperson said: “We have now provisionally had the warmest day of the year so far with 29.4C at Santon Downham in Suffolk.”

The UK Health Security Agency issued its first yellow heat-health alert this year, running until 8am on Sunday in the east and south-east of England, London and the East Midlands.

This means there could be an increased use of healthcare services by vulnerable people, including those over 65 and individuals with pre-existing health conditions.

The heat and humidity could spark “very severe weather” overnight, the Met Office meteorologist Aidan McGivern said.

The amber thunderstorm alert, covering parts of East Anglia and eastern parts of East Sussex and Kent until 5am on Saturday, advised of the risk of torrential rain, large hail, frequent lightning and gusty winds. The storms could lead to road flooding, difficult driving conditions, power cuts and flooding of homes and businesses.

Katharine Smith, the flood duty manager at the Environment Agency, said: “Environment Agency teams have ensured rivers and watercourses are clear ahead of the storms and stand ready to support local authorities in their response to surface water flooding.

“We urge people not to drive through flood water as just 30cm of flowing water is enough to move your car.”

Yellow thunderstorm warnings are in place for much of southern and south-western England and Wales between Friday afternoon and midnight. Another warning is in place across eastern and southern Scotland from midnight to 6pm on Saturday, with northern and south-western England and Wales also affected.