What is the furthest straight-line distance one can travel on the mainland?

Okay, let's talk about the geography of Great Britain and the longest straight shot you could take across the mainland. Great Britain, the largest island in the British Isles, has a pretty irregular shape, which makes calculating the longest straight line a bit tricky! Think of it like trying to measure the diagonal of a wonky shaped room. The distance from Land's End in Cornwall, the southwestern tip, all the way up to John o' Groats in the northeast of Scotland is often cited as the longest distance across the island, but that's following roads, not a straight line. The actual straight-line distance, if you could somehow travel directly through hills, cities, and everything else in between, is approximately 870 miles. This takes into account the curvature of the earth and the specific points that maximize the distance on the mainland. The other options are close, but they don't quite capture the true maximum straight-line distance possible on the island.