The "US States" topic prompts me to celebrate my 100th posting by asking a similar question about Britain - the eastern one is easy, but for the others it'll be necessary to find answers for (a) England (b) Great Britain (c) the United Kingdom (d) the British Isles.
Pedants may start hares running in all directions by considering whether embassies (and consulates?) are considered to be legally British territory.
I believe the most Southernly point is the Lizard, and the Western point is Land's End- therefore both in Cornwall.
I think the North question has been a question on Millionnaire, but I can't remember the answer.
ok. I've resisted the temptation to look at any map since seeing this tread for the first time.
some are guesses, and some I'm pretty confident about
England - north Northumberland, east Suffolk, south and west Cornwall
Great Britain - north Shetland, east Suffolk, south Cornwall, west Inverness (I'm hoping that includes the western isles)
UK - as GB, except west Fermanagh
British Isles - as UK, except west is a county of whose name I have no idea situated somewhere around Cork
Scotland - north and west as for GB, east Berwickshire, south Dumfriesshire
Wales - guessing on all four here and I might be mixing old and new county boundaries, north Gwynnedd, east Flint, south Glamorgan, west Cardigan
Northern Ireland - not even going to attempt this one
The easternmost point of the UK mainland is actually Lowestoft Ness. The northernmost tip is Dunnett Head, several miles west of John O'Groats and up a bit more.
I'd thought we were going for counties, rather like the US one was for states. But if it's actual locations, and we're confining it to the GB mainland, then southern extremity is Lizard Point, and western is Ardnamurchan Point (west of Fort William)
British Isles (if you include the Channel Islands), then in the north it's Yell I think in Shetland, west is either Rockall (dubious) or somewhere in Kerry (I'm told it's not Valentia, but it's out that way), south I'm not actually sure now I think about it, Jersey is it? East is of course Lowestoft.
For the UK, the west changes to (forgetting Rockall) St.Kilda most probably.