Succession: what if there's a lesbian Queen? (or a gay King)?

The UK's House of Lords is debating the Succession to the Crown Bill. One of the Conservative Lords Spiritual and Temporal has raised the issue of David Cameron's same-sex marriage legislation affecting the succession. The Telegraph reports that the peer wants to ban Royals in same-sex marriages, specifically asking:

"What happens if we have a lesbian queen in a same-sex marriage who conceives using an egg implanted with donor sperm? The law should be clear, but this is a question that has not been thought through in the Bill."

While the question may appear facetious, it underlines the absurdity of hereditary monarchy. It also highlights that this is a British institution - given that the New Zealand legislation is now on parliament's order paper, any amendment now in the UK could affect the other countries that have retained the British monarch as head of State.