I heard from one of my PI's to be a bit careful considering UK schools since their PhD length is only 4 years (likely because most UK students have a Masters before doing a PhD). Not that you still be rigorously trained but if you decide to do a postdoc at the United States, there may be some PI's not keen on taking you in since they believe you didn't get 'enough training'. Though I feel like that potential lab not accepting you would not be a good place to be in because you are still getting trained as a post-doc. Hope this helps!