Just to clarify this story slightly, on re-examination I see that on 1841 census Ann Cranwell and her parents are actually living next door to James Darton, not in the same house. Also, 1851 James and Ann have John and Mariah SAVAGE as neighbours, and in 1861 James and Ann are living next door to a farmer by the name of W. Dearman. In 1871 farmer Dearman has retired and the farm is now run by his nephew Charles SAVAGE. Other Savages on the census too, so makes me think James's wife Mary Savage was almost certainly related to them. Could it be then that Mary has run away, and her family know James is still married and so he's unable to marry Ann? No blame attributable to anyone, and the facts will almost certainly never be known.