As the Queen's health is placed under a media microscope it is hard to avoid thinking ahead with unwelcome and rather gloomy thoughts to a time when plans have to be made to crown her successor.

As I review my thoughts on Christian England (and the UK), the Crown, faith and the Church, a memory thrusts its way to the surface of my consciousness.

I was sitting in the House of Lords a few years ago talking to a Christian peer. He had a rather badly tuned hearing aid. But he was very interested in the same issues as we heard recently that a large group of French generals were giving thought to. Given the demographic changes in our society, was there any likelihood of civil disturbance or even civil war on our streets? You may remember that the French generals, to the serious infuriation of the media, thought that in France there might well be.

I tried to answer the question I was being asked, and the peer in question was having trouble hearing me, and asked me to speak up. I suddenly found my mind caught up with memories of Guy Fawkes, who smuggled himself into the cellars right underneath where our feet were, in the bowels of the House of Lords. The year was 1605 and he had planned to set off a bomb that would kill James I and allow for the possibility of restoring a Catholic monarch.

I told my friend to turn his hearing aid up as I was not going to raise my voice in that place and risk being half-overheard, perhaps misunderstood and accused of sedition, given the very delicate things we were discussing; and as I tried to shrug off the historical memory of the presence of Guy Fawkes.

In 1605 there were two competitive religious communities, both embodying alternative political as well as theological values, Catholics and Protestants.

Today there are more, but three constitute the largest communities: Christians, secularists and Muslims. There are many others obviously - Hindus, Sikhs, Buddhists, and others - but in smaller numbers.

All of this has significance as we consider the coronation of our next monarch and it's worth spending a moment on the historical origins of our coronation service as not many people are well-acquainted with these.

The earliest reference in English history to the anointing or consecration of an English king is found in the Anglo-Saxon Chronicle's entry for 787, which records that "Ecgfrith [was] consecrated as king." The next one was for the consecration of Aethelstan at Kingston-upon-Thames in 924, at which he was confirmed as ruler of a unified English kingdom of 'Saxons, Mercians and Northumbrians'.

It was under Aethelstan's nephew Edgar that the consecration rite would take its essential character and provide a pattern that would endure into the future. He was the first monarch to claim he was King over the whole of Britain and Edgar had a particular agenda. He gathered a circle of reforming monks such as Dunstan and Aethelwold around him at court, and allied himself with their attempts to oust corrupt clerks from the English Church's hierarchy. He intended to establish a uniform Benedictine rule throughout England. In return, the monks venerated Edgar as a Christ-like guardian of the Church.

Edgar's especially elaborate coronation took place at Bath in 973 and it was under him that the consecration became an expression of a cult of sacral kingship involving the idea that the monarch was specially chosen by God. The King, the priests and the people were unified in a shared faith under God and a shared civic identity, and as such, the coronation was an expression of a divinely ordered consensus between all three.

Down the centuries there were a number of changes and evolutions. Perhaps the most seismic was at the Reformation when the Bible in particular was given a more prominent role, and the monarch became more politically representative than divinely anointed.

King Edward VI was crowned with not one but three crowns – simply because the pope used three crowns, and the reformers wanted to make clear that the pope wasn't able to claim any kind of superior status.

King James II made a few temporary changes, getting rid of the Communion service, since as a Catholic neither he nor his wife could take part.

In the 18th century, as anti-Catholic sentiment flared up again, a more Protestant flavour coloured the words of the ceremony as prayers that the monarch would represent Jesus in this life were replaced with prayers that the monarch would faithfully serve Jesus in this life.

George IV went down-market a little and dressed all the guests in Elizabethan costumes and set guards on the doors to lock his wife out.

As such, the varying demands of the Reformation, the Glorious Revolution, the Enlightenment, and the Anglo-Catholic movement made their own adjustments, each reflecting the dominant tastes and preferences of the culture of their day, while also demonstrating a certain degree of cultural and ideological elasticity.

This historical input notwithstanding, the coronation essentially contains two elements: an invocation of religious blessing for the monarch, and an expression of the social and political contract.

Nothing has changed politically in the last few hundred years; we remain a monarchical democracy. But in the sphere of religion there have been two stark developments. The first is the emergence of a vigorous secular and atheist culture, represented perhaps most starkly in popular thought by the new atheism.

The second is the growth of Islam and the number of Muslims who are now citizens in the UK. This has taken place against the backdrop of a collapse in numbers of both those who identify as and who practise as Christians.

On the death of Queen Elizabeth II, the secular voice is likely to complain and criticise the religious component in the coronation of the future King Charles III. But there is not sufficient support for their position to be politically effective. However, in one of the more recent polls, a majority of people (57%) think that the ceremony should be Christian, compared with 19% who think it should be multi-faith and only 23% who think it should be secular.

Another critical number is that of religiously active Muslims. There has been no census since 2011, but Wikipedia estimates there were about three and half million Muslims in the UK in 2017, a figure that will have grown by the date of the Queen's death.

An assumption often made in establishing the numbers of those who are active in their faith and attend the mosque is to place the proportion at 50 per cent of the Muslim populations, which would give a very rough number of 1.5 to 2 million active Muslims.

The number of Christians in church at a rough estimate is judged to be about 5 per cent of the population which would be near 3 million. If these figures are anywhere close to accurate, it raises the question of what kind of religious component there ought to be in a coronation for it to be representative of the population?

There are groups in the country which take the view that Judaism, Christianity and Islam are at root the three 'Abrahamic Faiths' and constitute religious cousins, which overlap and complement as monotheisms. This view welcomes and celebrates multiculturalism and its presuppositions. There are many people, like Richard Harries, a previous Bishop of Oxford, who have long wanted to change the coronation service to a multicultural and multi- or inter-religious event that specifically reflects Islamic character and theology.

However, despite the superficial similarities within an overarching monotheism, the claims of Jesus and Muhammad are not compatible with each other. If one accepts either one of the two, the other of necessity is in error. The Quran takes the view that the Gospels are mis-representations or distortions of what actually happened to Jesus.

The theological presuppositions of the Gospel and epistle writers, on the other hand, are that if someone claims a revelation that involves denial of the unique Lordship of Christ and His resurrection, they are informed by a deceitful spirit and are mistaken. Orthodox Christians and Quranic Muslims recognise that they stand for two mutually exclusive revelations of God, despite having areas of overlap and things they hold in common.

If, for example, the two characters of 'God' are compared, one discovers that the nature of Muhammad's (more impersonal) Allah is very different and indeed some would maintain, contradictory, to that of the Jewish experience of Yahweh and His presentation of intimate but excoriatingly holy Fatherhood as Jesus offers access to Him.

The figures that Muhammad alludes to and references in the Quran - Adam, Abraham, Moses, Elijah, Jesus and Mary - are different historical and theological characters to those found in the Hebrew Bible and the Gospels.

Those who organise, and indeed are in the process of organising the future coronation service are faced with limited choices. Either bowing to the superior numbers of atheists and agnostics, they may choose to exclude the Christian character of the ceremony in favour of a political event which saves making the choice between competing and incompatible religions. Or they could create a fusion of different and contradictory religious elements on the basis of a multiculturalism which assumes moral and religious relativism, and risks protests from the conservatives on both sides. A third possibility would be to follow in the immediate footsteps of tradition and to remain exclusively and to some 'inhospitably' Christian.

The coronation will become a microcosm of the choice that faces the nation as a whole in other matters. The difficulty that presents itself is that despite all the white noise of relativism and multiculturalism, orthodox Christians and Quranic Muslims are both convinced that it is their duty to convert the whole world to the different revelations they embody. The bloodstained history of the last fifteen centuries is an indication of how seriously both take their own (different) self-understanding.

A further complication is that culture is shifting faster than ever before. Both Islam and progressive secularism are growing rapidly in influence and expectation. Paradoxically, the longer the Queen lives, the more problematic the handover becomes.

The coronation of King Charles III will provide a testing moment of truth for what have become the new stresses, strains and fault lines of Western culture in today's United Kingdom.

Dr Gavin Ashenden is a former chaplain to the Queen. He blogs at Ashenden.org