There are thirteen long distance routes in England & Wales which have been designated by the Countryside Agency as 'Official' National Trails. Ten of these are fully developed and three are still under development in places. The first National trail was the 412 km Pennine Way, opened in 1965. The longest is the Southwest Coastal Path which follows the coastline around the South West of England from Somerset in the North to Dorset in the South.
The ultimate long distance route is from John 'O' Groats at the North Eastern tip of Scotland to Land's End at the South Western tip of England. Many people have walked it more than once to raise money for charity, some have even walked it backwards (that's walking backwards - NOT Land's End to John 'O' Groats!)
C A Ridley