Sorry, Seb, but perhaps you need to keep up with history. The May Bank Holiday was historically asociated with Whitsun - and some calendars still call it that. It was only moved by a week or two when the May Day Holiday was introduced in the 70s; no-one was too keen on two Bank Holidays so close to each other.
Sorry, Hope but the non-secular Whitsun holiday is still practised in some countries on the correct date - just not in the UK.
The late Spring bank holiday in the UK is taken on the last Monday in May (with a few secular exceptions).
Sometimes it will coincide with Whitsun, but mostly it doesn't.
It was changed over 50 years ago from actually being Whitsun to not being Whitsun.
It was
not moved because of the introduction of the International Workers day holiday (that was in 1978, introduced by Michael Foot IIRC.)
It was officially moved in fact in 1971 under the Banking and Financial Dealings Act 1971, and that was following a trail period from 1965 to 1970.
So 13 or 7 years (depending on how pedantic you want to be) before the early spring holiday was introduced in fact.
Unfortunately, Hope perhaps it is you who needs to keep up with history?