The warning currently covers Dumfries and Galloway, and Lothian and Borders from Sunday and warns of danger to vulnerable people and transport infrastructure. The mercury could hit 30 degrees in Scotland by the start of next week.
It comes as a more serious red warning was issued for England for the first time, indicating a “danger to life”. Temperatures in the south of England may hit a record-breaking 40 degrees.
A Met Office spokesman said: “A hot spell is likely to develop from Sunday, likely peaking early next week, leading to widespread impacts on people and infrastructure.
"After a very warm night, hot weather, already underway across other parts of England and Wales is expected to develop more widely across Wales, southwest and northern England, plus southern Scotland. Some exceptionally high temperatures are possible, both by day and by night, for Monday and Tuesday. This following a warm weekend, will likely bring widespread impacts to people and infrastructure.”
Water shortage warning
It comes as Scottish Water has issued an urgent ‘save it’ plea after customers drained public supplies by 200 million litres extra last weekend, mostly through watering their gardens.
Road tankers have been drafted in to begin delivering supplies to parts of the country, such as the isle of Arran, beginning to show the first signs of drought.
And at the same time, the Scottish Environment Protection Agency reports that much of the east of the country is now in ‘moderate scarcity’ for water, the second-highest warning possible.
The seeds of the current water shortage were sewn last year. Scotland’s water authorities warned then that only significant rainfall over autumn and winter would replenish declining water stocks, which never materialised.
Last weekend over just two days, customers used an additional 200 million litres from their taps in their homes and gardens – the equivalent of 100 Olympic-sized swimming pools – as temperatures soared.
Scottish Water also say you should take shorter showers and turn the tap off when brushing your teeth.
There is no prospect yet of a hosepipe ban but Scottish Water said it was ‘closely monitoring’ growing public water consumption, which 'could put pressure' on supplies.
Kes Juskowiak, water operations manager, said: “The warm, dry weather has seen an increase in the amount of water being used by customers and the amount we need to put into the system to meet that demand.
“We will continue to monitor our reservoirs and other water sources closely. Continued warm weather, a lack of rainfall and continued high use levels in the home and garden could put pressure on supplies in the days and weeks ahead.
“We are doing all we can to maintain water supply to customers. That includes moving water around the network and where necessary bringing in additional supplies to communities via road tankers.
“I would ask that householders take a few simple steps to use water efficiently and use less wherever possible, but particularly in the garden.”
In the east of Scotland, the Dee catchment area as well as the Forth, Almond and Tyne areas have been raised to a warning for ‘moderate scarcity’ for water.
They join Aberdeenshire, Tayside and Fife in what is SEPA’s second-highest warning for water shortage.
In the west, the Clyde area has been elevated to ‘alert’ level, while the north west and Western Isles remain in normal conditions.