Today is an historic day for the British monarchy as the Succession of the Crown Act 2013, which introduces gender neutral succession in Britain and the other fifteen realms of which Elizabeth II is head of state, comes into force. The prime minister of the sixteen kingdoms agreed upon these changes at the Commonwealth Heads of Government meeting in Perth on 28 October 2011 and although it passed its final reading in the British Parliament and received the royal assent in April 2013 it has not come into force before now as it needed to be passed by the all the realms, which has been a rather complicated process. In the end Australia, Barbados, Britain, Canada, New Zealand, St Kitts and Nevis and St Vincent and the Grenadines have passed legislation to amend the succession, while Antigua and Barbuda, Bahamas, Belize, Grenada, Jamaica, Papua New Guinea, St Lucia, the Solomon Islands and Tuvalu concluded that it was not necessary to pass legislation, apparently because the succession was not codified in suc detail. For instance, the constitution of Tuvalu appears to say that whoever is monarch of Britain is monarch of Tuvalu.
While younger brothers have until now bypassed elder sisters in the act of succession, the first-born will now be the heir regardless of its gender. This change will be retroactive, but only for those born after 28 October 2011. Thus Princess Anne is still behind her younger brothers and their children in the line of succession, and Prince Edward's son is still ahead of his older sister, while Senna Lewis, a granddaughter of the Duke of Gloucester, overtakes her younger brother Tane, who was born after that date.
The new Succession to the Crown Act also means that people who marry to Catholics are no longer barred from ascending the throne, while Catholics themselves are still excluded as the monarch is required to be Anglican. This change is retroactive, so that the Earl of St Andrews (the Duke of Kent's oldest son), Prince Michael and several others are now back in the line of succession (while Lord St Andrews' children and his brother Lord Nicholas Windsor, who are themselves Catholics, are still excluded).
The new act also repeals the Royal Marriages Act of 1772, scrapping the requirement for anyone in line of succession to seek the monarch's permission to marry. This will now only apply to the first six people in line to the throne. Currently those six are Prince Charles, Prince William, Prince George, Prince Harry, Prince Andrew and Princess Beatrice, which means that Prince Andrew's eldest daughter needs permission while her sister does not (the birth of Prince William's second child, which is expected in the second half of April, will however push Princess Beatrice out of the top six).
Of the seven European kingdoms, Spain is now the only one left where sons still take precedence over daughters in the order of succession. Gender neutral succession was first introduced in Sweden in 1980, followed by the Netherlands in 1983, Norway in 1990, Belgium in 1991 and Denmark in 2009.