Pennine Way<---link i found. might have some information for you.
so it's a 267 mile trail. lot easier than the Appalachian trail, which is over 1000, and with no drastic inclines or declines. looks like a pretty nice (not to mention scenic) 3 week hike. i read alot about distance hiking because i hope to do that one day. so the average hiker can cover at least 20 miles a day comfortably and someone in pretty good shape that is used to hiking and exercising consistently can do anywhere from 30-40 miles a day. they suggest that you REALLY plan it out by getting geological maps of the entire trail and mapping out when and where you'll be on certain days so that you can send food packages for yourself to post offices and such. the best weight of food to carry is 7-10 days worth. anything more and you're in trouble (this i know from personal experience).
hope some of this helped. anyhow, looks like an awesome hike, Have Fun and let us know if you end up doing it. i would love to hear about the trip.