*aside* what is the deal with the unwritten constitution of Great Britain? How do you know what is guaranteed when it is unwritten?

It's easy enough ... we don't.

There have been campaigns many times for a written constitition for the UK. Maggie Thatcher dismissed a campaign in her time with words that were more prophetic than she realised: "Some of the worst abuses of the law and human rights have been carried out by countries with written constitutions."