The thing is, there is nothing Islamic about a caliphate/state. There is not a shred of theological, historical or empirical evidence to support the existence of such an entity. Yes, Muslims have a romanticised view of Medina, under the rule of the Prophet Muhammad between 622 and 632AD, but it had none of the trappings of a modern state - no fixed borders, no standing army, no civil servants - and was led by a divinely appointed prophet of god. Unless the shadowy al-Baghdadi plans to declare his prophethood, too, the Medina example (should anyone be reading for it) is irrelevant.
Incidentally the caliphate (from the Arabic khilafah, or "succession") that came after Muhammad was plagued by intrigue, division and bloodshed. Three of the first four "rightly guided caliphs" were assassinated. By the 10th and 11th Centuries, there were three different caliphates - Umayyad, Abbasid and Fatimid - which were constantly at war with one another. Not quite the golden age of the Islamist imagination.
Second, the Islamic faith doesn't require an Islamic state. Muslims have never needed to live in such a caliphate in order to pray, fast or give alms. And, as the great Muslim jurist of the 14th century Imam Shatibi argued, sharia law can be boiled down to the preservation of five things: religion, life, reason, progeny and property. I'd argue that the UK, despite rising Islamophobia, does preserve these five things and therefore allows Muslims to live "Islamic" lives. By contrast, the authors of a recent
study at George Washington University found: "Many countries that profess Islam and are called Islamic are unjust, corrupt and under-developed and are in fact not 'Islamic' by any stretch of the imagination.
Third, most Muslims don't want an Isis-style state. In their book Who Speaks for Islam? I would hazard to guess that the popular Muslim opinion would sound something like not wanting religious leaders to hold direct legislative or political power.
Fourth, time and again, politicised Islam has proved to be a failure. Violent Islamists have discovered, after the shedding of much blood, that you cannot Islamise a society by force - whether in Afghanistan, Gaza, Egypt or Iran. Rhetoric is easy; running public services and state institutions much harder. The hand-choppers and throat-slitters of Isis, Boko Haram, al-Shabab and the rest have no political programme, no blueprint for government. Theirs is a hate-filled ideology, built on a cult of victimhood and sustained by horrific violence.
A good book called
The Rise and Fall of al-Qaeda by Fawaz A Gerges gives such an example.