Dear Paul,
It is not a bad idea to complaint to the Spanish Ministry , but in my opinion these complaints will not go very far.
I think that complaints about serious offences from agents, developers should be directed via court actions, I know t is more expensive and slow but much more efective. The cheaper option is the written complaint at the consumers protection offices which are located in every Council, with this you are guaranteed a written answer by the authorities. But be careful: when you do it have the proofs available.
Another good option is to report in media, send letters to news papers, contact a local ( or not so local ) radio station, report in places like Spanish Property Insight is also very helpful.
About lawyers: the best possible action is to contact the local lawyers association, in spanish we call them Colegio de Abogados, they are the official bodies that regulates the legal practice in Spain, you can leave your complaint there. There is a Colegio de Abogados in every province.
Of course you can also report about your lawyer at the consumers protection offices and if it is a serious case start a legal action.
I hope this information helps, regards,
Jose Maria Sánchez Alfonso
Abogado / Lawyer
Costa del Sol
Málaga
jmsalfonso@inicia.es
95.2479268