Isn't LEGO (or their parent company?) buying Merlin? If that counts, well, that's most of the active theme park scene already being taken over already. Doubt much will happens on an operations level, though.
I don't see BPB selling themselves out to anybody, isn't that park a family-owned business? I mean, with new generations, things could change, but I don't think anything is likely in the foreseeable future.
Maybe Drayton Manor or Flamingo Land could be bought in theory, but as far as I know they're doing okay as it is, and I don't think they are particularly attractive to the big chains anyway. Drayton Manor faces competition from Alton Towers, and Flamingo Land is too far away from the major population centers.
And as for the rest of the UK parks, they would all need significant investment to become worthy competitors in the national market. That makes them pretty unattractive for the major chains. Parques Reunidos in particular tends only to buy parks that are "readily developed" and already have a large share of the regional market. I bet the other chains have a similar philosophy. If the park doesn't have that market position, there wouldn't be much of a point in buying it. Maybe chains would be interested in BPB, but again, I don't think they're selling.