Monday is expected to bring the hottest weather of the week, with a surge of hot air moving north from France ahead of an approaching Atlantic low-pressure system.
Southern and eastern parts of England will widely reach low to mid-30sC, with a few locations across London and the Home Counties likely to reach 34C.
Much of the Midlands, East Anglia and southern England will see temperatures reach around 30C or above, while eastern parts of Wales will also experience unusually hot conditions.
Scotland, Northern Ireland and western Britain will experience cloudier skies with outbreaks of rain as low pressure slowly moves across Ireland.
Overnight into Tuesday, rain in northern and western areas is expected to become locally heavy and thundery.
Further south, most places will stay dry, warm and humid, although a few thunderstorms could develop across south-east England.