The heatwave is expected to see temperatures rise day on day over the long weekend, eventually peaking with record-breaking highs of 26C on Sunday and 27C on Monday.
Gosport in Hampshire reached 25.5C on Saturday – making it the UK’s hottest day of the year so far, according to the Met Office.
While it did not beat the record of 29.4C, set in Camden Square, London, in 1949, it was warmer than the Canary Islands (21C) and Barcelona (17C).
Scotland and Northern Ireland enjoyed the warmest Saturday of any Easter weekend on record, with 23.7C and 21.7C respectively. Wales hit 23.5C.
The records for the rest of the Easter weekend are now within reach. In 2011, Solent in Hampshire reached 25.3C on Easter Sunday and 24C on Easter Monday.
Met Office meteorologist Sophie Yeomans said: “It won’t be one of the hottest temperatures we have had in April, but it is going to break some of the records for Easter Sunday and Easter Monday.
“Into Sunday we may get a 26C somewhere across the UK and for Monday probably up a degree or two again, 26C or 27C.”
The hot weather is thought to have caused a huge fire on Ilkley Moor in Yorkshire on Saturday evening.
Fire crews from across Yorkshire responded to the blaze across 50 acres of moorland and used beaters, leaf blowers and portable pumps in an attempt to extinguish the blaze.
— Martyn Hughes NYFRS👨🚒 (@Har_DistrictWM)April 20, 2019
Hay fever suffers have also been warned of a “deadly pollen bomb” which could put people with asthma at risk of a potentially life-threatening attack.
The pollen count is forecast as high for most places until Tuesday and in the southeast until Wednesday.
Sonia Munde, of Asthma UK, warned sufferers to take hay fever and prescribed medicines and to keep their blue reliever inhaler with them at all times in case of an emergency.
On Good Friday, temperatures hit 24C in some parts of the country, warmer than Rome (22C), Barcelona (21C) and Malta (18C).
The warmest temperature ever recorded on an Easter Friday was 26.9C at St James’ Park in London in 2011.