Although temperatures will remain lower than the record-breaking highs of 40.3C (105F) seen last month, this latest hot spell is expected to last much longer.
High pressure building across the UK could lead to temperatures of 35C (95F) – and the heatwave is expected to peak on Friday or Saturday.
The warning of the heatwave in Britain comes as much of Europe is baking in record heat, which has exposed riverbeds and triggered restrictions on water use in many areas.
Britons are now being urged not to host barbecues in the tinder-dry conditions, with fears fireworks and sky lanterns could spark ‘large-scale’ fires in parched areas, according to Sky News.
Retailers are also facing calls to ban sales of disposable barbecues.
In southeast England, where water suppliers have faced most pressure so far, just 4.2mm of rain fell in July.
That beats a record that has stood for 70 years, and by a huge amount – July 1952 saw three and a half times more rainfall than last month.
On Saturday, 15 homes were evacuated after a garden fire got out of control in Essex – with “multiple gardens, sheds, and outbuildings” destroyed and a dozen properties damaged.
The whole of England and Wales is set to feel the effects of the heatwave as high pressure builds – ‘with sunny and very warm if not hot’ conditions in Scotland and Northern Ireland as the weekend nears.
In the Netherlands the level of the Waal – the main Dutch branch of the River Rhine – has dropped below the bottom marker on a bridge at Nijmegen, BBC News reported.
The city lies near the German border, and the Rhine is a key artery for cargo vessels and ferries.
Newly exposed stretches of the Waal reveal dumped bicycles, car tyres and other detritus.
Parts of the IJssel river, flowing north, are now so narrow that a ban has been imposed on ships passing each other. And the heat has caused toxic algal blooms to flourish in parts of the Maas and Waal rivers, so people have been warned not to swim there, and to keep their dogs out of the water.
The south of Spain is well used to scorching summers – but Andalusia is also one of Europe’s main agricultural regions, and crops need irrigation in dry conditions.
In northern Italy an unexploded Second World War bomb emerged from the dried-up River Po. It was detonated in a controlled explosion on Sunday. The 450kg bomb was found by fishermen.