Thanks SJPC
The Runners World version I have has 3 options.. a Beginners, an Improvers and an Achievers training plan. I'm doing a bit of a hybrid... between the Beginners and the Improvers. But the surprising thing is that for the Beginners (for those aiming 4.5 to 5.5 hrs), the longest run is 165 minutes, a month before the race.
If you're running at 5.5hr pace, that's 12.6 minutes per mile.. so you only do 13.1 miles. For the Improvers, the same calculation works out at a maximum training run of 16.5 miles. This worries me!
Anyway, I'm ignoring that bit... I've done a 17miler and plan a 19 this weekend and a 22 next week. Good luck