One couple made the most of the warm spell to tie the knot on Brighton beach in East Sussex amid bikini-clad babes.
Office workers in London basked in the lunchtime sunshine as the highest temperature of the year in England so far this year of 18.6C (65.4F) was recorded at Heathrow, west of London.
That beat the previous year high in England of 18.1C (64.5F) registered in Writtle, Essex, on Tuesday, which wasn't quite enough to top the Britain-wide year high of 18.7C (65.6F) in Braemar, Scotland, back on March 17th.
The warmest temperature of the year so far in Wales of 16.9C (62.4F) was registered in Cardiff.
But Met Office forecaster Alex Burkill warned people to make the most of the warmth as some areas could even see snow before the week's out.
Mr Burkill said: "The relatively warm weather is not going to last.
"Wednesday was probably the best day in terms of temperatures for a while.
"Thursday will be a similar sort of day with some showers around. Temperatures will reach 17C, maybe 18C. Further north it will be cloudier and cooler, but largely dry.
"But by Friday things are going to get more complicated.
"We have a warm front coming up from the south and a cold front coming down from the north, so Friday won't be a good day weather-wise.
"There will be rain, some heavy, and some areas in the north could see some wintry elements - sleet or even snow.
"There will be some rain overnight on Friday, but it should clear away into Saturday, and Sunday should be mostly dry for many."
He added: "It doesn't look like temperatures will be as warm over the weekend, with a high of around 12C (53.6F)."
Variable amounts of cloud and some reasonably warm sunny spells, the best of these in the south. Some showers around, with more likely to develop during the afternoon, particularly in the warmer, brighter south. Light winds through the day. Maximum Temperature13 °C.
Becoming mostly dry with light winds and clear spells. Becoming cold with a chance of grass frost in the north. Thicker cloud in the south later with perhaps further showers. Minimum Temperature 2 °C.
Chilly with some dry conditions initially, just a few showers. Persistent rain is likely to move southwards later, perhaps turning to snow on hills. Feeling colder with overnight frost following. Maximum Temperature 9 °C.
Outlook for Saturday to Monday:
Saturday, cold with bright spells and showers, some wintry over hills. Frost overnight. Mainly dry Sunday and Monday but with increasing amounts of cloud, and gradually becoming less cold.