Welcome to the big unknowns! As it happens, the CAA and a liaison group are having a chat through this and other issues tomorrow morning... Current policy (rightly or wrongly) is that UK non-EASA full licences will not be issued alongside UK issued EASA licences - the NPPL is separate since it is not an ICAO compliant licence. Those who held UK National licences pre-JAR retain them as a privilege, while those of us who started with JAR and progressed to EASA licences on JAR expiry do not. It is rather unclear at the moment whether UK policy will be to allow the issue of UK National licences on the basis of EASA licences from next year onwards, or whether the 2 systems will separate in their entirety - ultimately it is a political decision rather than a CAA or EASA one.
As an existing UK EASA licence holder I will be able to gain a National licence next year if I choose to change state this year, on the basis of existing UK tests passed etc. It is therefore logical that if you train with an ATO holding both UK and EASA approvals, and test with an Examiner holding both EASA and UK licences and Examiner authorisations - assuming the two do split next year - with paperwork and applications to both then your training and tests will be recognised by both the UK and the IAA. I and my colleagues (and indeed our Ops Inspector, poor man!) started having these conversations this morning about how best to protect future licensing without jeopardising what we do at the moment, not easy times.