Try and find out if your dentist practice is a member of the BDA (British Dental Association) Good Practice scheme. If they are, then you can complain to the BDA if you have a problem.
There is a link here to find dentist practices in the scheme:
http://www.bdasmile.org/smile/about/index.cfm? contentid=1445
Or you can contact this lot if you have a complaint about a private dentist:
If you have a complaint about private dental services, you should contact the Dental Complaints Service.
This is a service funded by the General Dental Council, which sets out standards of conduct and regulates all dental professionals in the UK.
You can call the Dental Complaints Service on 08456 120540