Britain will today bask in temperatures up to 10C higher than the seasonal average, forecasters said.
The heatwave is expected to hit the south hardest, with predicted maximum temperatures of 21C (69.8F) in Berkshire, Surrey and Hampshire. The temperature is expected to be similar or hotter than in Spain, with Barcelona and Madrid expected to reach around 19c on Saturday. The UK will also be warmer than in Portugal and Turkey.
Paul Mott, forecaster at MeteoGroup, the weather division of the Press Association, said that temperatures will be well in excess of expectations for this time of year.
"There will be plenty of warm sunshine for most areas of the UK, and the highest temperatures will be around 20-21C.
"Across much of the UK temperatures will generally be around 15-19C.
"We're up to 10C above the seasonal average."
Mr Mott said the highest temperatures tomorrow will be in Aberdeenshire, which is expected to reach 20C (68F).
It will be less warm in southern England, but still around 18C (64.4F).
The pleasant conditions caused by high pressure are expected to continue into next week, with no significant drop in temperatures until next weekend.
"It's looking fine and warm for much of the coming week," Mr Mott said. "It will last until until at least Thursday or Friday and will probably be milder next weekend."
He described the current spell of warm weather as "quite unusual" for March, and warned there was no significant rainfall in the drought-affected areas of southern England.
Helen Chivers, a meteorologist at the Met Office, also said that the unseasonal weather would continue into next week.
"We are expecting the warm weather to carry on into the weekend and next week. We may well see a change towards the end of next week with things becoming cooler, but it is quite a long way out for us to say for definite that this will be the case," she said.
Meanwhile the gardeners at Cornish National Trust mansion Cotehele are celebrating as the peak blossom time of their daffodils has coincided with their annual weekend celebrating the plant.
A spokesman said it is the first time in four years they have got their timing perfect for the two-day event.
"It will be a fantastic chance for garden lovers and families to see our wonderful collection of historic daffodils, including some varieties which are 200 years old," said senior gardener Aimee Kingdom.
The gardens are open from 11am to 4pm.