Simon
A simple way of looking at the various sectors ('denominations') of the Christian faith in the UK is to first distinguish between (Roman) Catholics, like yourself, and Protestants. The Protestants split away from the (Roman) Catholic church during the Reformation in the 15th-16th centuries (16th century in the UK).
You can then further divide the Protestants into the Church of England (Anglicans), which is the established church of England with the monarch (queen or king) as 'supreme governor', and the "non-Conformists" - a term that can be applied to all other Protestants. The non-Conformists split away from the Church of England at various times and include Baptists, Methodists, the Society of Friends ('Quakers'), Congregationalists, Presbyterians and others. The church of Scotland ('the Kirk') is effectively non-Conformist by this definition and by their practices and beliefs.
You are quite right to suggest that there are other Christian denominations in the UK. These tend to be smaller than those named above and include the Lutherans (who are mostly in northern Europe).
There are also small Christian communities who are neither Roman Catholic nor Protestant. These would include the Greek Orthodox church, the Russian Orthodox church, the Bulgarian Orthodox church. As the names imply the members of these churches are mostly (but not entirely) people of non-British nationality or their descendants who have retained the faith of their parents and grandparents.
I hope that this is helpful. It is an attempt to compromise between being too detailed and over-simplifying!
Regards