Temperatures have soared to over 29C in parts of London, making it the warmest April day for nearly 70 years.
The unusually warm weather across the UK is the result of low pressure over the Atlantic and high pressure over western Europe drawing in warm air.
Thursday's high of 29.1C was recorded at St James's Park in central London during the afternoon, making it the hottest UK day in April since 1949.
The average maximum temperature for the UK in April is 11.9C.
The highest recorded temperature for this month was 29.4C back in 1949 in London.
Pollen levels are high throughout much of the UK, with BBC Weather warning it could be "uncomfortable" for hayfever sufferers.
Runners in Sunday's London Marathon have been warned to expect hot weather, with suggestions it could be the hottest race on record.
Event director Hugh Brasher said contingency plans were already in place which included providing extra water supplies along the route for drinking and for competitors to douse themselves with.
The heat caused the cancellation of a horse race at Cheltenham but those over shorter distances went ahead.
The high temperatures come on the same day as Debenhams blamed freezing weather in late February for a fall in sales and profits.
This temperature comparison tool uses three hourly forecast figures. For more detailed hourly UK forecasts go to BBC Weather.
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