Forecasters have issued severe warnings of thunderstorms on Saturday.
A yellow weather warning is in place until 1pm on Saturday in south-west England, with a risk of flooding, damage to buildings, lightning strikes, hail or strong winds – as well as a small chance of travel delays and cancellations of train and bus services.
Northern Ireland, Scotland and northern England, in contrast, will enjoy sunshine and balmy temperatures on day three of the bank holiday weekend.
The Met Office meteorologist Steven Keates said the overall picture for the UK showed big contrasts as Scotland recorded its warmest day of the year on Friday at 21.6C.
The mercury is expected to continue rising in Scotland to a high of 23C in the west Highlands on Saturday, accompanied by “a lot of sunshine”.
After downpours were forecast throughout Saturday morning, southern England is expected to see some “respite” before a return to “severe” weather overnight.
Thunderstorms developing over parts of England and Wales – including London, Manchester and Cardiff – from early on Sunday may cause travel disruption and, in a few places, flooding. A yellow warning is in place until 6pm on Sunday.
“It will be late evening so I think for events in London I wouldn’t want to completely discount a shower for, say, the party at the palace. I think at the moment it looks like a mostly dry picture and quite pleasant conditions,” Keates said.
“There’s a sort of north-south split in our weather over the weekend with southern areas bearing the brunt of a couple of rounds of heavy rain showers and thunderstorms and areas farther north seeing fine, dry and some warm and sunny weather as well.
“So quite big contrasts across the UK but for some of us the weather could cause a few problems over the next couple of days and, at the very least, be inconvenient given there’s lots of outdoor plans and festivities I expect on many people’s minds.”
In Northern Ireland, Saturday is expected to bring warm temperatures of around 19C and sunshine with a bit of cloud towards the south.
Cloud will arrive in southern parts of Northern Ireland on Sunday, potentially carrying a risk of rain.
Friday brought sudden, heavy downpours to Wales, with the seaside town of Criccieth recording 92mm of rain in six hours, leaving homes and businesses damaged and some roads impassable.
