The effect of Letters Patent creating peerages can he changed by legislation which has that specific effect. It cannot be changed by legislation of general application. Thus, the Peerage Act 1963 allowed Peeresses in their own right to sit in the House of Lords regardless of the terms of any Letters Patent creating the peerage. The House of Lords Act 1999 removed the right of anyone to sit in the House by virtue of a hereditary peerage unless they were specifically excepted from the provisions. Conversely, the House of Lords decided in 1922 in the case of Viscountess Rhondda that the terms of the Sex Disqualification (Removal) Act 1919 were not sufficiently specific to allow her to take her seat in the Lords when her Letters Patent allowed her to inherit the peerage, but not the seat in the Lords. I am aware of only one case in which the effect of individual Letters Patent has been changed by Act of Parliament, which is that of the Duke of Marlborough in 1706.