Under ecclesiastical law, a marriage within the prohibited degrees was not absolutely void but it was voidable at the suit of any interested party. For this reason, Charles, the younger brother of Jane Austen, was able to marry his deceased wife's sister in 1820 and to remain married to her until he died in 1852. The Marriage Act 1835, however, hardened the law into an absolute prohibition (whilst, however, authorising any such marriages which had already taken place), so that such marriages could no longer take place in Great Britain at all. Such marriages from that date had to take place abroad: see, for example, William Holman Hunt and John Collier, both painters, who married the sisters of their deceased wives in Italy and in Norway respectively. But this was only possible for those who could afford it..................................................
The Deceased Wife's Sister's Marriage Act 1907 removed the prohibition (although it allowed individual clergy, if they chose, to refuse to conduct marriages which would previously have been prohibited). But the Act did exactly what it said and no more. So, for example, . it was not until 1921 that the Deceased Brother's Widow's Marriage Act 1921 was passed). Relationship Act 1931 extended the operation of the 1907 Act to allow the marriages of nieces and nephews by marriage as well.
Hope this makes things clear!
