At the moment there are no formal qualifications required for TAs but my Head has informed TAs at our school that relevant TA qualifications will shortly be a requirement. My advice would be to get a qualification whilst you are volunteering. TA jobs are becoming harder to obtain and schools receive many applicants for every post. At my school anyone without either a teacher qualification, a degree or an NVQ3 were not considered. There were so many applications the Head could afford to be picky. All schools are different and my school pays all TAs at level 3 and has two full time HLTAs paid at HLTA rate. Other schools employ TAs with a wider range of skills and qualifications. Most TAs at our school look for a local provider for NVQs and study in the evenings. You could speak to the TAs in your school and ask them if they have any idea of local providers of NVQ training. Good luck with your search for a job.