Yellow heat health warnings have been issued across much of England with forecasts saying temperatures may climb to as high as 32C (90F) on Tuesday.
All areas of England, except the North East and North West, are covered by the warnings from the UK Health Security Agency (UKHSA), which are in place until Wednesday.
The agency said the hot weather may have “significant impacts” on the health and social care sector, particularly across the South East of England and London.
The Met Office has separately issued a yellow alert for thunderstorms later in the week which covers most of England and parts of Wales.
The UKHSA has warned the hot spell may make an “observed increase in mortality across the population likely, particularly in the 65-plus age group or those with health conditions, but impacts may also be seen in younger age groups”.
Temperatures could reach as high as 32C in London and the south east of England on Tuesday, BBC Weather said.
Many parts of the country will experience temperatures four-to-five degrees warmer than average for this time in July, the forecaster said.
Only the far north-west areas of Scotland and parts of Northern Ireland will see some cloud and possibly rain on Monday and Tuesday.
The hottest day of the year so far came on 19 July when a temperature of 31.9C was recorded at St James’s Park in central London.
It is possible that a few places in England and South East Wales will reach heatwave criteria, where temperatures exceed the Met Office defined temperature threshold on three consecutive days, which varies depending on where in the UK you are.
In the London area that threshold is 28°C. For Scotland, Northern Ireland, Wales and most of northern and western England it is 25°C.
If nowhere in Scotland reaches 25C on Tuesday, it will be the first July since 2010 that temperatures there have not reached this level.
The drier weather for much of the country is expected to break on Thursday, when a yellow warning has been issued by the Met Office for heavy rain and thunderstorms.
Most of southern England, the Midlands, parts of Wales and much of northern England are covered by the alert, which warns of “lightning, hail and gusty winds” that could lead to some disruption.
It comes into force at 00:00 BST on Thursday and ends at 23:59.
The rest of the month is expected to bring breezy conditions to the north west, and drier and brighter weather to the south east.
A more widely settled period is expected towards the middle of August.
