Posted: 16/04/2014 at 15:51
a couple of (hopefully helpful) things:
felt tired during race & a HM in 1:32 seven days before the marathon are probably linked. The old adage of take a days recovery for every mile raced means that you shouldn't have 'raced' a HM within two weeks (or 13 days) of the marathon.
the problem with flat marathons is the constant loading of your muscles, where the loading varies when going up & down hill. This means you wanted to do some long runs (in time as much as distance) to get your legs used to the consistent pattern of the flat surface.
Your London experience sounds similar to mine last year, two contributing factors were drinking too much water (causing stomach cramps) primarily due to being unaccustomed to the heat after training early on cold & damp winter mornings. Could this apply to you? Maybe look to
It doesn't sound like you followed the P&D plan very loosely, as you mention a few sub-MP paced runs on the flat, and your hard effort seven days before the race. You might get better results if you follow it more closely as it sounds like you made a few mistakes that their plans are designed to avoid.