My father's from Pakistan and he has been a secularist all his life. In the Pakistani context, there's no messing with religion. There's been a battle for the soul of Pakistan since 1947 and I have grown up without any illusions about the dangers of religious power in the context of a country like Pakistan.

I realized that the ignorance was profound. I don't mean that in a pejorative sense, it's just that people didn't know what the Shari'a was, as such. They knew that it was something good. I should say perhaps that the Shari'a, etymologically in Arabic, means a desert path to water. It means a path towards salvation, in the seventh-century context, to the desert people. If you have a path to water, that's the path you want to take to get you where you want to get to; where you should get to. And that much was clear but beyond that people didn't know what the rules were.

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.

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.

There's crucial distinction that has to be drawn between the Shari'a, which is this hugely expansive vision of cosmic order that I've been describing, and principles of Islamic law, known in Arabic as "Fiqh" - a word that means understanding. If you're a devout Muslim, you don't argue against the Shari'a; the Shari'a is the path that God has laid down. But what you can do, and what people are doing all the time, is arguing over the correct interpretation of the Shari'a, arguing over the Fiqh. That's something that has been going on throughout Islamic history.

In 1979, you had the revolution in Iran. You had the Hudood Ordinances in Pakistan, which are the laws that are notoriously used against women, which are theoretically used against thieves although they're never carried out - an actual amputation or an actual stoning. The blasphemy laws, again, never actually carried out, though they're there, heavy with menace on the statute books.

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.