If and when the EASA changes take place it will not matter a jot whether you hold a UK National issued PPL or a JAR complient one. The advice has not, from the CAA anyway, been to change to a JAR licence prior to the proposed changes.
This is entirely incorrect. An EASA licence may be issued only on the basis of the equivalent JAA licence and not a UK national one. That is, you will be able to exchange a JAA licence for the EASA equivalent but if you hold only a UK national licence you will be required to meet the EASA requirements for licence issue, including obtaining a pass in the relevant EASA theoretical knowledge examinations and skill test(s).
The UK CAA has been pressuring UK national licence holders to obtain JAA licences since at least November 2007 and are now refusing to issue examiner authorities to the holders of UK national licences, advising applicants that they must first obtain a JAA licence.