I agree with Send Clowns, but I think his post is uncharacteristically unclear - sorry mate!
Hour-building - as SC says, you need 150 hours total time before you can start a CPL course. You can build these 150 hours any way you like, anywhere in the world you like.
JAR CPL - you need to follow an approved course, the CAA document provides details of everyone who is approved by the CAA.
JAR IR - you need to follow an approved course, the CAA document provides details of everyone who is approved by the CAA. The test itself needs to be done in the UK, so you'll need to do at least part of the training in the UK so that you're familiar with the local airspace.
The best thing to do is to invest in a copy of LASORS, which costs £10 (I think), order direct from the CAA. It's also available free, on-line. That contains all of the requirements for every UK-issued license and rating. Unfortunately, with open-ended questions like yours, it's too complicated to be able to get everything into a short post.
FFF
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