Parts of Britain basked in weather warmer than mainland Spain and Ibiza as temperatures reached over 20C (68F) today.
London was the hottest part of the country, with temperatures reaching a maximum of 20.4C (68.7F) at St James's Park at 1pm, according to the Met Office.
This made the capital hotter than Madrid (17C/62.5F), the Balearic Islands (18C/64.5F) and the French Riviera (16C-17C/61F-62.5F), weather forecaster MeteoGroup said.
Other parts of the south east of England will see the best of the conditions today, reaching between 17C (62.5F) and 19C (66.2F), meaning plenty of time in the sun for some on the first day of British Summer Time (BST).
The balmy weather will remain for much of the week ahead, according to Met Office meteorologist Eleanor Crompton.
" It will be warm but temperatures may be a down a couple of degrees. We'll see more cloud and hazy sunshine around with temperatures in the late teens from Monday to Wednesday."
Ms Crompton added: " There is a chance of some thundery showers coming up in western and central areas tonight, spreading to the north. It's the u sual case of warm weather followed by the increased risk of showers."
The weather is being driven by hot air currently over the Low Countries, according to senior forecaster at MeteoGroup, Rachel Vince. Belgium and the Netherlands are forecast to have temperatures in the mid-20s Celsius today.
The springtime temperatures are also good news for Britain's plants and animals.
Matthew Oates, wildlife adviser at the National Trust , said: "We've just suffered one of the most miserable winters ever - the wettest on record, if one of the mildest. The weather owes us and nature a great Spring.
"This warm spell is great news for butterflies as they soak up the sunshine, fluttering through gardens and parks, and brilliant for birds as they get ready for the breeding season and fill the air with sweet music. If the sunny weather continues through the week it's also good news all round for blossom on fruit trees and that classic symbol of Spring, the bluebell."