You know what, I have never really gotten it sorted out as to the British Isles, the United Kingdom, Great Britain, etc...anyway, Wikipedia tries to help with its colored lines but I probably still won't 'get it' permanently...
I also looked to see how long the British Isles have supported human life, and there is an article in The Guardian talking about 900,000 years, give-or-take, although continuous human habitation for 'only' 12,000 years or so.
Point being, with all those people over all that time, it's no wonder that everybody might have to be just buried on top of each other, and get dug up every time today's folk build something new! Here is that article from The Guardian, followed by the colored lines getting the British Isles figured out; the Republic of Ireland not being part of anything, it's just on its own! https://www.theguardian.com/science/2010/jul/07/first-humans-britain-stone-tools