The route

I have mapped the route for the day out using Google Earth, which you can view by looking here. The route consists of the London Marathon route, followed by the return journey split onto 10 sections spanning between the intervening villages (where I will meet up with Jen to replenish my pack). I have worked out approximate timings (which should be an overestimate if anything), and they look something like this (the pages correspond to Book 2 of the Greenwich Meridian Trail book by Graham and Helda Heap):

Time	Section	Dist	Pages
06:00 - 07:00	Drive from St. Ives to Redbridge tube station
07:00 - 08:00	Tube from Redbridge to Greenwich Park
08:00 - 09:45	Marathon preparation
09:45 - 13:45	Run the marathon!	26.2
13:45 - 16:00	Walk/run through London to join the GMT	31.1
16:00 - 19:30	Run through London to Waltham Abbey	48.9	4 - 21
19:30 - 22:00	Run to Stanstead Abbot	58.1	24 - 31
22:00 - 00:30	Run to Standon	67.1	31 - 37
00:30 - 03:00	Run to Wyddial	75.7	38 - 41
03:00 - 05:00	Run to Royston	82.9	42 - 47
05:00 - 07:30	Run to Orwell	91.6	48 - 53
07:30 - 09:30	Run to Hardwick	99.2	54 - 57
09:30 - 11:30	Run to the guided busway	106.6
11:30 - 12:30	Home straight into St. Ives	112.3
12:30 - 14:00	Celebrate and fundraise in town