From the current examiner's handbook (version 2006/7, dated 01/07/06, page 29):
For SEP and TMG revalidation by experience, irrespective of when in the last 12 months the experience requirements have been met, the ANO requires that revalidation should only be carried out during the 3 months before expiry.
Mad, but there it is, and it does say 'in the last 12 months', although elsewhere reference is made to the 12 months preceding expiry. Solution: 'Bloggs, your previous rating expired today, it is replaced by this one which runs from today....' Happy?
Agreed £35 sounds a bit steep, I think our school charges £10 if non-member, free otherwise.