Hi Whopity,
I really don't think the outcome of the Referendum is going to change the UK's involvement in EASA. There are a number of non-EU countries who are in EASA, I think the UK will stay in even if leaving the EU.
Taken to its silly extreme and assuming independence for all areas wishing it, there will be an English CAA, excluding Cornwall and Yorkshire of course. We'd have the KAA (Kernow Aviation Authority). UKIP is a force in the land West of the Tamar.
More seriously, it seems the only check the CAA have on exam passes is when a Course Completion Certificate is submitted. They depend upon an examiner interpreting the 18-month rule as above, not sure all would do so in the same way...
An on-line exam system will wash all these issues away.
TOO