it will depend on the consent form signed and what the doctor discussed with you. Have you followed the formal NHS complaints system? if so, they will have told you that your next recourse if you are not happy is to go to the health care commission (an independent body who can follow up for you) however, i suspect you have left it too late.
As to whether you would be successful in suing them, i cannot say, you would have to consult a solicitor (at your own expense) who specialised in medical cases. You cannot go to the HCC and use a solicitor at the same time, so you might want to investigate the free option first.
If you are asking for opinions (no law qualification, but a lot of experience of working n the NHS) i would say i don't think you are likely to be successful for a few reasons
1) you have left it too long
2) operations can have side effects that were probably explained to you at the begining. You have just been unlucky it didnt work for you, and in retrospect probably wish you hadn't had it done. it dosent sound on the face of it that anyone has been negligent - just that the operation didnt work as you and the doctor had hoped. if there is no negligence, i cant see you being successful
Anyway, if you do decide to persue it it might help if you were clear in yourself what it actually is you are complaining about - ie is it that they did something you didnt consent to, or is it because the op hasn't worked?