If you have a "calendar" on a pc/on the wall you can set simple reminders in advance.
Last Sunday March = start of BST - clocks go forward 1 hour - shut heating down and switch on immersion.
Last Sunday October = end of BST - clocks go back 1 hour - start heating up and switch off immersion.
You will, of course, appreciate that the precise implementation of these routines and/or duration between them may vary according to a number of factors - mainly commentary by others in residence and whose decision maybe likely to prevail. Since 2018 "shut down" @ Casa Flonska - deferred until 10/04/18 - other than 3 "test" fire ups (one very recent) - see:-
https://www.theanswerbank.co.uk/ChatterBank/Question1622998.html
"We are in the pipe - five by five" for GMT day . . . well . . . possibly?