"it is roughly 380 miles across"

That's what it says on the site, but to make it that, they must have taken a fractal path- the distance as the fly crows is about 160km, say 100 miles. The path must be like a mediaeval pilgrimage, two steps forward, one step back.

" but we are just going to do hull - manchester which is about 110 miles, so 220 in total with the return journey."

From what I know of the area between Manchester and Liverpool (which is quite a lot: I was brought up there) you won't be missing much.