An amber weather warning for extreme heat has been extended by the Met Office, with forecasts suggesting temperatures could reach 38C (100F) in parts of England later next week.
An updated warning will now be in force from 01:00 BST on Monday through to 23:59 BST on Thursday, reflecting growing confidence that exceptionally hot and humid conditions will continue through the middle of the week.
Large swathes of England and Wales are covered, though more northerly areas are only under the warning on Wednesday and Thursday.
The warning means population-wide impacts are likely, including serious health risks, disruption to daily routines and increased pressure on infrastructure.
Daytime temperatures are expected to exceed 30C (86F) widely across the warning area, with the hottest locations potentially reaching around 38C (100F).
Overnight temperatures are also forecast to remain unusually high, with some urban areas struggling to fall below 20 or 21C (68-70F), resulting in so-called tropical nights.
The heat is spreading from continental Europe where an extremely intense hot spell has developed.
Temperatures in parts of western France could climb to 43 or 44C (109-111F) over the next few days.
Paris is likely to reach 40C (104F) which would be unprecedented for June.