Brisk south-easterly winds developing on Tuesday and Wednesday will drag in much warmer air from the European continent.
Temperatures will be around 6 to 10C above average for early April.
On Tuesday temperatures will rise to the high teens and low twenties in most parts.
Across the south Midlands and the west coast of Wales it is likely to reach 22C, making it the warmest day of the year so far.
The previous highest temperature this year was 20.9C, recorded on 31 March at Pershore, Worcestershire.
Tuesday will be a mostly sunny day, especially across England and Wales but cloud will build in Northern Ireland and western Scotland with a few showers.
By Wednesday temperatures will rise even further to 23C, perhaps even 24C in south-east England.
With sunshine continuing, temperatures across England and Wales will still be into the low twenties, so it will feel more like a typical summer’s day for most of us.
However, conditions will turn a little cooler in western Scotland, Northern Ireland and Irish Sea coasts with more cloud and rain moving in later in the afternoon.