Is it possible for a Roman Catholic to be elected Prime Minister of the United Kingdom?
Roman Catholics in Britain and Ireland received the franchise in c1830s following the safe passage of a Bill in the House of Commons to extend voting rights to Catholics. The Bill of Catholic Emancipation was put into parliament by the Duke of Wellington when he was prime minister – the bill was passed but it cost him his premiership. A Catholic can most certainly become prime minister. It really depends upon the mass electorate of Great Britain and especially of England who are for the most part classified as CofE or just plain Protestant. A Catholic may not sit upon the throne of England and the monarch may not marry a Catholic. This will not change, the people of England would not allow it. There are an estimated 2 million Catholics in UK.
There is nothing to stop a Catholic becoming Prime Minister. However, Tony Blair is not a Catholic. His wife and children are Catholic, but he is Church Of England. There has never been a Catholic Prime Minister of the UK. Disraeli was born Jewish, but converted to the Church of England at an early age.