Parts of the UK could see temperatures reach as high as 28C on Thursday, making it the hottest day in April for a number of years.
The unseasonably warm weather is being caused by low pressure over the Atlantic and high pressure over western Europe drawing warm air to the UK.
The average maximum temperature for the UK in April is 11.9C.
According to BBC Weather, if temperatures peak at 28C they will beat the warmest April day in 2011 where highs of 27.8C were seen at Wisley in Surrey.
The highest recorded temperature for this month was 29.4C in 1949.
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 on route both for drinking and for competitors to douse themselves with.
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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Pollen levels will be high throughout much of the UK, with BBC Weather warning it could be “uncomfortable” for hayfever sufferers.