If you're "departing from an airport in the UK on any airline" then I'm pretty sure the legal minimum compensation is more than that:
* https://www.caa.co.uk/passengers/resolving-travel-problems/d...
* https://www.caa.co.uk/passengers/resolving-travel-problems/d...
It sounds a bit confusing as to whether you were cancelled or delayed, or accepted an offer etc. but I wouldn't accept $24...