1. 25°C has been reached or exceeded somewhere in the UK in 27 of the last 145 years in April.
2. There were eight such days in April 1893.
3. 26.7°C (i.e. 80°F) has been reached or exceeded somewhere in the UK in only four years ... 1865, 1893, 1945 and 1949.
4. There were five such days in April 1893.
5. Hottest April days, with the warmest place that day, are as follows:
16th in 1949 29.4°C at Camden Square (London)
18th in 1893 29.0°C at Stratfield Turgis
20th in 1893 28.9°C at Cambridge
21st in 1893 28.1°C at Ross-on-Wye
24th in 1893 27.8°C at Cambridge
25th in 1893 27.8°C at Cambridge
17th in 1949 27.8°C at Whitstable
27th in 1865 27.4°C at Camden Square
16th in 1945 27.2°C at Camden Square
23rd in 1874 26.5°C at Greenwich
25th in 1984 26.5°C at Onich (nr Fort William)
6. That 26.5°C at Onich in 1984 is Scotland's highest in April.
7. Last time 25°C was reached was 30th April 1994.
8. In April 1903 the highest max for the UK was just 17.2°C at Cambridge ... the record lowest highest.
9. Last year's highest appears to have been 23.7°C at Enfield.
10. There was only one 25+ day between 1902 and 1933, there were 17 between 1934 and 1955, and only one between 1956 and 1983.
These are complete to the best of my knowledge, but as always there may be one or two omissions.