you are worrying too much...
With the present JAR-PPL a pilot may already fly within Europe since they are recognised by each European country. This licence will automatically become a EASA ppl after April 8. You can continue your present training and after April 8th you'll receive the new licence. The CAA licence is only for the UK, it is NOT a JAR or EASA licence (thus for you of no interest).
Normally the country of residence issues the licence. So if you live in Spain, the Spanish authorities issue it. But if your home is the UK, then I think you may have to change it over to the CAA registry (I'm not sure 100% myself here... I'll have to look it up myself).
In your case, continue training for your JAR-PPL and don't worry (yet) about what happens after April 8th. There will be a transition period for some already issued licences, which may be the other dates that confuse you.