Now you tell me!
Distance though hasn't been my problem: from Strava, and ignoring my 'normal' runs, in the last 9 weeks I've run a 20 miler around Sutton Bank, 21.8 miles around the 3 Peaks, another 21 mile triangle of the Dales, 27.6 miles over legs 1 and 2 of the BG (2 days after my first canal half marathon run), 16 odd miles around upper Wharfedale (2 days after my second canal half mara), 10 miles around the Fairfield Horseshoe, 21 miles around the Edale Skyline (3 days after my third canal half mara), 20 miles up and around Ingleborough with just last weekends long 'un (a recce of the TWA) cut short by bad weather leaving my longest run at 8 miles.
They were all in the hills though. I think I needed a 20 plus mile flat run at a half decent pace, goddamit!