The Bank Holiday sunshine - which saw temperatures of over 20C in parts of Scotland - is expected to stick around for today before a front bringing cloud and rain pushes in from the West.
Chills of 5-6C will be felt in most cities north of the border on Wednesday and Thursday.
Met Office Forecaster Helen Roberts said highs of 28C (82.4F) were expected on Tuesday, with southern England seeing the warmest conditions, but the UK as a whole faces a “massive drop in temperature” as the week progresses.
Scotland, Wales and Northern Ireland are expected to be cooler, with maximum temperatures around 15C.
From Wednesday, it will be “nowhere near as warm” as the Bank Holiday temperatures, Ms Roberts said, with temperatures struggling to hit 20C (32F) and most likely resting in the mid teens.
On Monday afternoon the mercury hit 28.7C (83.6F) in Northolt, west London, making it the hottest early May Bank Holiday Monday and weekend since records began.
Those hoping for a repeat scorcher next weekend will be disappointed, as it is forecast to be “decidedly cooler and more unsettled than the one just gone”.
Looking ahead to the royal wedding, the forecast is proving elusive, with Ms Roberts saying there was “lots of uncertainty and low confidence surrounding the conditions” on May 19.
She said the weather would most likely be changeable.