Thought I'd just make a quick update, again might be of interest to someone now or in the future.
After the initial antagonistic texts, 3 or 4 days passed then we received a polite email stating he would like to come over to 'chat'. We agreed but not hopeful of a favourable outcome based on passed experience. In the meantime we contacted building control and had a good conversation with one of the inspectors there who confirmed that based on our description that it did contravene regulations and was very supportive and said they will come out to provide a free inspection. The builder came over today and we was prepared for a battle but he was largely apologetic and while not completely wanting to personally admit the error he was at least willing to finally accept responsibility for making it right. As
@Notch7 suggested the roof really needs to be ripped off and completely re-done as a warm roof if possible. Maybe he saw that post as that's what he proposed, to our relief. Also, the coping stones will be all coming off and the top layer being replaced with fibreglass. He wants to come back in March to do this work which we agreed to.
So, assuming nothing crops up to change those plans that will be the best possible outcome as things stand and is definitely a load off the plate after chasing this for almost 3 years now. Thanks to all those that gave their opinions.