Plainjayne, as phineyj says so accurately, non-teaching experience is not always valued very highly in TA / teacher recruitment.
So the main barrier to your recruitment as a TA may not be that you are 'over-qualified', but that you have insufficient in-school experience and skills.
I only mention it because it is easy to assume (if you are 'non standard' as an applicant) that the problem lies in the thing which makes you non-standard - in this case, your previous qualifications and work experience. I know that I have fallen into the same thought process in the past, to be put right by a wise and experienced HT.
In fact, the problem may simply be that you lack the things they may be looking for - previous experience as a TA, TA qualifications, extensive experience working with children, even in some cases knowledge of particular conditions (for 1 to 1 TA / support roles) or of particular interventions that the person who used to have that job delivered.
Recruitment in schools, as in other organisations, is very much based on 'what are we looking for' -type paperwork - the match between the role and the person's skills and competencies. If you have lots of other things in your past that don't fit on the tick sheet, that's not a problem as long as you also tick everything that they werre looking for. However, if you don't tick enough of the things that they are looking for, you won't get the job - not because the things that you have over and above the job description count against you, but because there are not enough things that count for you on the tick sheet IYSWIM?
TA interviews will usually involve an observed task with children, as well as an interview, btw.