There is no recency requirement on SEP Class aeroplanes after differences training has been carried out.
PPL(A) means Private Pilots Licence (Aeroplanes). The 'Group A' nonsense is routinely spouted by some 'PFA coaches' (actually, they are CRIs) to differentiate between SEP Class aeroplanes and Microlights because they either cannot be bothered to keep up with the times or just aren't capable of doing so. And yes, I do have a 'thing' about people using the right terminology - precision is vital in aviation as any engineer should accept.
The BMAA have no say in any JAR-FCL licensing matter; nice chaps that they are, they are purely concerned with UK PPL(M) licences and/or NPPLs with Microlight Class Ratings.
You may NOT fly a microlight on a lapsed JAR-FCL SEP Class Rating unless you have also obtained a NPPL with Microlight Class Rating - in which case the validity of that licence's Microlight Class Rating (currently 5 in 13 - but soon to be changed) will regulate your Microlight flying.
Your simplest solution is to maintain your JAR-FCL SEP Class Rating and use that for either SEP or Microlight flying. But you MUST meet the SEP Class Rating re-validation criteria to keep flying either SEPs or Microlights on a JAR-FCL SEP Class Rating.