This argument about what is or is not a proper licence is dragging on far too long.
Read LASORS 2003 edition, section A, page 3, which lists those states which were JAR fully approved in October 2002. You will see that the Czech Republic is amongst them, with approval for JAR FCL 1 and 3, which means that fixed wing training is approved.
So far as the source of licence issue is concerned, it is irrelevant. There is effectively no such thing as a Czech JAR licence or a UK JAR licence. They are all identical JAR licences, simply issued in different states. Anyone desperate to have "UK" on a licence can do so by following the procedure outlined in LASORS section A, page 10, which explains that the state of licence issue may be changed if a pilot works or resides in a state different from that of licence issue. There is only a small fee for this.
If a pilot has a licence issued in one state and wishes to add a rating, this can be done in any other state. This was the whole idea of JAA in the first place. So, you can fly your G-registered aeroplane until you run out of objections to the idea of cross-state acceptability. Let's hope that it won't be too long before we in western Europe are able to accept that people in other places can actually do the job just as well as we can, whatever the arguments are on pricing.
I am not on commission, but may I commend LASORS to those who want authoritative answers rather than supposition and rumour?