I remember this well. April 1990 started off very mild with temperatures in the high teens but within a couple of days, an Arctic airflow comes southwards and brought snow showers. I recall snow showers falling during the evening of the 3rd April and woke up the next morning with a snow cover. Only the the second official snow cover for the 1989-90 season recorded here.

Maximum on 1st April 1990 at Manchester was 17.4C by the 3rd it was 7.0C

 There was a notable earth tremor for the UK on the 2nd April with its epicentre at Bishop's Castle in Shropshire with a magnitude of 5.1 

I think the biggest switch around temps I remember was April 1981.