Parts of Yorkshire were pelted with hailstones the size of a £2 coin during thunderstorms.
Photographs posted on social media showed people in Leeds and Sheffield cradling handfuls of the icy precipitation.
The "large" hailstones in the images appeared to be between 3 and 4 cm in size, a Met office meteorologist said.
A yellow weather warning for thunderstorms and rain is in place for much of the UK until 09:00 on Saturday.
Hailstones are formed when drops of water freeze together in the cold upper regions of thunderstorm clouds.
Craig Snell, a meteorologist with the Met Office, said those seen in winter were "quite small", but heat in summer months gives thunderstorms more energy.
This "helps keep the hailstones up in the clouds for longer, they get to grow more and then fall from the sky," he said.
The thunderstorms follow on from the heatwave on Thursday, when temperatures reached 33.4C (92.1F) at Heathrow Airport in west London.
Temperatures on Friday reached a maximum of 31.2C (88.16F), recorded at Kew Gardens in west London, the Met Office said.
It warned up to 20mm of rain could fall in an hour in areas covered by the yellow warning, but said the storms were expected to clear towards the north east on Friday evening.