There is an ongoing debate about whether the Act should be amended to eliminate its clear gender discrimination. The Act provides that the eldest son of the heir to the Throne is next in line for succession. This means that if Prince William and Kate Middleton have a daughter and then a son, the son would leapfrog his sister. (Queen Elizabeth II did not have any brothers.) The proposed amendment would provide that the eldest child is always next in line.
Here’s the twist: such an amendment would require the consent of all Commonwealth countries that recognize the Queen as their head of state. In effect, that Act of Parliament would also work a change in the domestic law of those countries. Thus, negotiations must be undertaken to secure consent from those former colonies, though of course they could refuse and start recognizing someone else as head of state (a President, for example).
This is the closest equivalent to an Article Five amendment in the British Constitution. You need support from Parliament and ratification by other legislatures. I think that issues involving the Crown are the only ones that require this special treatment.
No word on whether Parliament will also disestablish the Anglican Church and allow Catholics into the royal line. Gender discrimination is bad. Religious discrimination — not so much.