Protestantism (part of Christianity) is the largest religious demographic in the United Kingdom.
Before Protestantism reached England, the Roman Catholic Church was the established state church. Scotland, Wales and Ireland were also closely tied to Roman Catholicism. During the 16th century, the English Reformation and the Scottish Reformation in differing ways resulted in both countries becoming Protestant while the Reformation in Ireland did not enjoy the same degree of popular support.
Islam is the second-largest religion in the United Kingdom, with results from the 2021 Census recording just under four million Muslims, or 6.0% of the total population in the United Kingdom. London has the largest population and greatest proportion (15%) of Muslims in the country. The vast majority of British Muslims in the United Kingdom adhere to Sunni Islam, while smaller numbers are associated with Shia Islam.
During the Middle Ages, there was some general cultural exchange between Christendom and the Islamic world. Nonetheless, there were no Muslims in the British Isles; however, a few Crusaders did convert in the East, such as Robert of St. Albans. During the Elizabethan age, contacts became more explicit as the Tudors made alliances against Catholic Habsburg Spain, including with the Ottoman Empire. As the British Empire grew, particularly in India, Britain came to rule territories with many Muslim inhabitants; some of these, known as the lascars, are known to have settled in Britain from the mid-18th century onwards. In the 19th century, Victorian Orientalism spurred an interest in Islam and some British people, including aristocrats, converted to Islam. Marmaduke Pickthall, an English writer and novelist, and a convert to Islam, provided the first complete English-language translation of the Qur'an by a British Muslim in 1930. Under the British Indian Army, a significant number of Muslims fought for the United Kingdom during the First and the Second World Wars (a number of whom were awarded the Victoria Cross, Britain's highest honour). In the decades following the latter conflict and the partition of India in 1947, many Muslims (from what is today Bangladesh, India and Pakistan) settled in Britain itself.
Hinduism is the third-largest religious group in the United Kingdom, after Christianity and Islam. It is followed by just over one million people (around 1.7% of the total population). According to the 2021 United Kingdom census Hindus are primarily concentrated in England, particularly in Greater London and the South East, with just under 50,000 Hindus residing in the three other nations of the United Kingdom. Hindus have had a presence in the United Kingdom since the early 19th century, as at the time India was part of the British Empire. Many Indians in the British Indian Army settled in the United Kingdom of Great Britain and Northern Ireland.
Most British Hindus are immigrants, mainly from India, and there are also significant number of Hindu immigrants from Sri Lanka and Nepal, with even smaller numbers from Afghanistan, Bangladesh, and Bhutan. In recent decades, due to the efforts of ISKCON, BAPS and other Hindu organisations and increased interest in Yoga, Meditation and other practises associated with Hindu traditions, many British citizens have embraced Hinduism, including many celebrities. The UK has the largest Hindu population in Europe.
The right to freedom of religion in the United Kingdom is provided for in all three constituent legal systems, by devolved, national, European, and international law and treaty. Four constituent nations compose the United Kingdom, resulting in an inconsistent religious character, and there is no state church for the whole kingdom.
In 2023, the country was scored 4 out of 4 for religious freedom.