Here is an article with information:
http://www.dailymail.co.uk/debate/article-2811883/Cameron-son-turned-away-local-crimper.html
(At the bottom)
It's ironic that the 2nd Marquess of Bath disowned his eldest son Viscount Weymouth for marrying a local girl (I think the daughter of a gamekeeper or tenant). Viscount Weymouth died just before his father, so the next son became 3rd Marquess of Bath. That Viscount Weymouth never had any children, which relieved the family. I'm not sure whether it was in the power of the 2nd Marquess to cut off a grandson (I think the property was entailed upon the grandson). By contrast, the 1st Marquess of Exeter was able to marry a farmer's daughter, but only because he had already inherited the property and title. (His own mother was a French actress). Some interesting marriages even back then.
Shinjinee