Hi my dad is Polish but born in u.k after ww2 - his fathers surname is kaiser his mothers is Grobel?
Were your Grandparents married in the UK ?
You don't actually say if your Grandparents moved to the UK before or after WWII
You should be able to sort some of this out by using British Records... Naturalization Records etc.
We can't do much without dates and place names. More info, please.