UAV689
Basically correct.
Your JAA PPL will automatically transfer to an EASA PPL. The CAA will let you fly a Permit aircraft on your EASA licence, so no problem there.
The problem is that the hours flown on the RF3 will not count towards the currency on an EASA PPL. In the second year you will either have to fly 12 hours in an EASA-type aircraft or do an LST with an examiner.
That might also mean flying a completely different type and that may require additional training. The LST will involve a short nav ex.
Clever eh?