By Friday, the area of high pressure will shift further northwards, allowing the heat to spread further north and west into parts of southern Wales and the Midlands, with temperatures in the low to mid 30s.
At the same time, a developing easterly breeze will bring slightly cooler conditions to more eastern areas.
For Northern Ireland and Scotland, temperatures are expected to reach the mid 20s Celsius by Friday.
Amber heat health alerts are in place across parts the Midlands, eastern and southern England until 12 July.
Yellow heat health alerts are also in force across northern England for the same period.
This means that significant impacts are likely across health and social care services, including a rise in deaths, particularly among people aged 65 and over or who have health conditions.
On Wednesday, the National Fire Chiefs Council (NFCC) said the dry and hot weather meant there was an increased risk of wildfires, and advised people to avoid using disposable barbecues in open countryside, park and moorlands.
