Ayatollah Khomeini issued a fatwa to that effect, which was then given effect in the Islamic Republic of Iran, so in the Islamic Republic of Iran, it's flexible enough to allow for sex changes, and it encourages sex changes. But if you want to change your religion in Iran, you've got some serious problems. There are other problems. You're allowed to change sex, but if you want to be a homosexual, theoretically at least, you face the death penalty. Quite how often these penalties are carried out is a moot point, but it's there on the statute books.

If Muslims want to take their disputes to religious arbitrators because they genuinely believe that it's a matter of great spiritual importance that they do that, they shouldn't be the only community in this country that's denied the opportunity to do that. Because the Jewish population has been entitled to take their disputes to tribunals known as the Beth Din for over one hundred years, and the Church of England is integrated into the fabric of this country, and there are ecclesiastical tribunals where religious disputes can be dealt with.

The first rules about Islamic law weren't even written down for a century and a half after the Prophet's death, and it was another five centuries, half a millennium, before they assumed anything like a definitive form. So there have always been huge arguments over what Islamic law actually requires. There are four main schools of law in Sunni thought and there's a separate school of law in Shia thought, so these arguments do take place.

One of things that surprised me when I was in Iran was to find out that the country finances seven times as many sex change operations as the entire European Union. And the reason for that is because Ayatollah Khomeini himself, in the early 1960s, in the same time that he was developing this other idea of an Islamic state, also hit upon the idea that if a person is born into the wrong sex, it was entirely proper for them to change sex.

There were periods in Islamic history when things like apostasy and blasphemy were made punishable. So you know it kind of depends - there's no argument, quite apart from the question of the divine or otherwise nature of the Qur'an, that huge swathes of Islamic law are man-made. Clerics here - in maintaining their power, will often try to elide that and say "Well no, actually this isn't man-made at all. Stoning is part of the divine revelation." It isn't in the Qur'an but the way this has been done over the years is to take the Hadith.

Shari'a is not just the Qur'an, you see Shari'a is comprised according to all the doctrines. There's consensus and analogy - argument by analogy. These are the four components in the Shari'a. An orthodox Sunni would not accept that the Shari'a was simply comprised of the Qur'an itself and actually there are people who say that it's heretical to believe that. They have to say that because if they don't say that then they would have to accept that, for example, stoning is not a punishment which appears in the Qur'an - it doesn't.

I didn't quite know whether I was writing for the non-Muslim or the Muslim, and at the end of the day I'm writing, I hope, for people who are interested, whatever their faith. Even if they don't have any faith. As a barrister I had certain advantages - I could think like a lawyer and I knew how all the laws were fitted together and all the rest of it. One of the things I realized pretty early on while I was writing book about Shari'a was that that was as much a hinderance as it was a help because the Shari'a isn't just a system of rules.