Temperatures in the week ahead are likely to soar to up to 10 degrees above the average for this time of year, a forecaster said today.
Londoners will enjoy warm weather this weekend, with the mercury rising to up to 25C on Saturday, MeteoGroup UK, the weather division of the Press Association, predicted.
Temperatures are then likely to return to the May average of 15C next week.
Other forecasters have suggested the warm weather this week could be the start of a glorious summer.
Aisling Creevey, forecaster with MeteoGroup, said: "For the rest of the week it's looking warm with temperatures well into the 20s.
"At the moment the winds have changed direction, moving south-westerly, and the origin of the air is warmer."
She added: "But next week is likely to move back to the average for May which is about 15C to 16C in southern parts."
Ms Creevey said the whole of the UK and Ireland will experience a steady increase in temperatures this week, with Scotland and Ireland likely to hit up to 19C.
But the country will not escape a little rainfall, with mist and fog also predicted in western and northern parts.
Predicting the weather months ahead is notoriously unreliable. The Met Office predicted a "barbecue summer" for 2009, which was ultimately a washout.
The Met Office has dropped long-term seasonal forecasts in favour of monthly prediction for Britain, updated weekly.
But independent forecaster Positive Weather Solutions (PWS), which accurately predicted last year's wet summer, have forecast great weather for the months ahead.
Jonathan Powell, senior weather forecaster with PWS, said: "The pattern through June is unlikely to be all that stable, so expect some rain as we pass through mid-month, although again, there will be some pleasant sunshine from time to time, keeping temperatures on the warm to possibly very warm side."
He went on: "July too starts on an unsettled note, with some rain around, but summer will emerge, and we can expect some decent drier spells and some warm to very warm temperatures."
Of August, he said: "Towards mid-month, there will still be some pleasant weather around with long spells of sunshine."
Temperatures have been several degrees below average in recent weeks thanks to cool north-westerly winds, plunging as low as minus 6C in Altnaharra in the Scottish Highlands last week.