The Met Office has issued a rare red warning for extreme heat, indicating a risk to life in parts of central and southern England and Wales on Wednesday and Thursday.
An amber warning is in place for a smaller part of the UK until midnight Tuesday, with a new amber warning covering a larger area from that point until the end of Thursday.
The Met Office said temperatures are expected to reach 38C (100F) in London on Wednesday and Thursday, with forecasters expressing "growing confidence" that this week could break the record for the hottest June temperature of 35.6C (96F), set in Southampton in 1976.
Met Office meteorologist Jonathan Vautrey said: "It's particularly across central southern regions, where we have an extreme heat warning, an amber extreme heat warning issued, where we could see quite widely amongst the population some heat-related impacts throughout the week. Temperatures climbing towards the mid-30s in places, that is quite exceptional for June."
The Met Office issues weather warnings color-coded according to the expected impact and likelihood of those impacts occurring.
Yellow warnings are issued when low-level disruptions are likely, such as travel delays in a few places, with severe impacts possible but not expected. Amber warnings indicate an increased likelihood of disruption, including travel delays, road and rail closures, power cuts, and a potential risk to life and property. Red warnings signal dangerous weather is expected, with a very likely risk to life and substantial disruption to travel, energy supplies and infrastructure.
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