There is. If you are complaining about your own solicitor, contact the Legal Ombudsman on 0300 555 0333 . If the complaint is about someone else's, contact the Solicitors' Regulatory Authority on 0870 606 2555 (Information from the Law Society's website)
However, before you even consider going to the Ombudsman, you must put your complaint in writing to either the Senior Partner or the Complaints Partner. If you don't do that the Ombudsman won't deal with until you have done so.
It is important, as has been said, that you first give the practice that the solicitor is a member of the opportunity to resolve the issue. If you are still dissatisfied contact the Legal ombudsman on the telephone number Fred has provided.