Scotland and Northern Ireland will also see temperatures in the high 20s and could reach official heatwave criteria by Friday, the forecasters said.

Warming conditions in the UK have prompted the Met Office to raise the temperatures that have to be reached for an official heatwave for eight English counties.

In its warning, the Met Office said the wider population could experience adverse health effects including sunburn or heat exhaustion (dehydration, nausea, fatigue) and other heat related illnesses.

Additionally, it said increased visits to coastal areas, lakes, rivers and other beauty spots will lead to an increased risk of water safety and fire-related incidents.

Some delays to road, rail and air travel are possible, the Met Office added.

With the latest heatwave coming after months of low rain, which have left the countryside and urban parks and gardens tinder-dry, households in some areas are being urged not to light fires or have barbecues.

The Met Office’s fire severity index, an assessment of how severe a fire could become if one were to start, is very high for most of England and Wales, and will reach “exceptional” for a swathe of England by the weekend.

Scientists say the likelihood of droughts occurring is becoming higher due to climate change, driven by greenhouse gas emissions from burning fossil fuels and other human activities.

Dr Leslie Mabon, lecturer in environmental systems at The Open University, said: “Above all else, the drought risk we are seeing in the UK is a reminder that we urgently need to tackle the problem at source: this means reducing emissions from fossil fuels to limit the extent of harmful climate change we will face.”