I recently asked my solicitor for all my case file as I had been told they keep back information by Citizens advice. This was correct they had cads and medical reports that would have helped me in court. Would this be considered neglect I was on legal aid.
Gather all your facts together and contact the Law Society. Solicitors have a strict code of conduct, they need to explain why they witheld information - there may be a perfectly reasonable explanation but you should find out.