In 2018, the Mormon Church appointed a new leader. Retired heart surgeon Russell M Nelson was installed as its new president; at 93, it's only realistic to assume that his tenure may not be very many years long.

Mormonism has a much wider following in the US than in the UK, where its tenets are not widely known. So who are the Mormons – and are they Christians?

1. Mormons belong to the Church of Jesus Christ of Latter-day Saints. According to the Church's website, 'Mormonism describes the doctrines of the Church that were restored to the earth through the Prophet Joseph Smith.'

2. Smith (1805-1844) was the Church's founder. He claimed to have been led to a book of buried golden plates containing the story of an ancient American civilisation. The 'translation' of these plates was the Book of Mormon, published when he was 24 years old. By the time of his death he had accumulated tens of thousands of followers. Smith was killed when a mob stormed a jail where he had been imprisoned for destroying a printing press that had published criticisms of him. The golden plates, he claimed, were returned to the Angel Moroni and are no longer in existence.

3. The Book of Mormon is regarded as 'another testament of Jesus Christ' in addition to the Old and New Testaments, according to the Mormon faith.

4. Mormons believe the Christian church fell away from the original pure doctrines of Jesus and that Joseph Smith was sent to restore it. They reject the historic Christian creeds. They do not believe in the orthodox Christian Trinity, preferring to speak of the 'Godhead': 'Latter-day Saints believe God the Father, Jesus Christ and the Holy Ghost are one in will and purpose but are not literally the same being or substance, as conceptions of the Holy Trinity commonly imply.'

5. Mormons believe their 'apostles' receive revelations from God: 'The First Presidency (consisting of the president or prophet of the Church and his two counselors) and members of the Quorum of the Twelve Apostles receive inspiration to guide the Church as a whole.'

6. Women cannot be priests, though they can preach and lead congregational prayers.

7. Mormons have not practised polygamy since 1890, though it is still found in fundamentalist splinter groups.

8. Mormons practise baptism for the dead, but deny that this controversial practice amounts to post-mortem conversion: 'According to Church doctrine, a departed soul in the afterlife is completely free to accept or reject such a baptism — the offering is freely given and must be freely received.'

9. Mormons believe they will be reunited with their families when they die: 'Church members understand that families are the most important unit of society. Accordingly, those who follow Christ and keep His commandments are promised to live with their families forever in divinely instituted eternal relationships.'

10. Mormons have an unorthodox view of the Atonement, stressing Jesus' experience in Gethsemane, and of salvation, believing it must be partly earned.

So, are Mormons Christians? They use much Christian language and many of their spiritual practices are close to mainstream evangelicalism – prayer and study, for instance. They are socially conservative and place a high value on ethical behaviour. In that sense they are 'Christian'.

However, they do not believe Jesus was the Son of God in the orthodox Christian sense. They do not believe in original sin or in the orthodox Christian view of salvation and atonement. The Book of Mormon is another Testament on a level with the Bible, which Christians would deny. They believe the historic Christian faith has been corrupted and that Joseph Smith was a genuine prophet.

So it's fair to say that Mormonism comes out of the Christian tradition. But though they are adamant they are Christians, they cannot be accepted as such by the worldwide church because they have departed so far from the faith.