I am doing the same as you just because it is only a few grand more to do both. I got dual citizenship through my mother. Do your dual ATPL at a ground school then you can get your EASA Meir and CPL with a flying school in the UK as plenty offer it.
It is very little difference between just doing a UK licence and it opens yourself up to Ryanair and you can easily fly in Europe for a couple of years to build up hours if you struggle to get a job in the UK. It isn't a waste at all.
On current prices I got my course to 54k based on minimums. Doing the vast majority of my hours at my local aerodrome then going down to London to finish off my ratings.
As others have said you need a dual medical as well but first just get a CAA then you can do the EASA one at a later date.
Your PPL will only be valid in the UK as all you will have on your EASA licence will be an IR rating and CPL.