What would be a perfect schedule then? Ideally you’d be coming into a schedule where you’re already doing 35mpw based around a 2hr run on the weekend, a club night run Weds night and some easier paced running around those 2 sessions. Maybe the odd Parkrun and 10k or HM if during the summer or the odd XC race during the winter. This would allow you to start doing 2hr+ runs as your long runs fairly quickly and without any likelihood of picking up injury.
I would say that mid-week semi-long runs (13-15 miles) are the 2nd most important session of the week followed by a speed session and the rest of the week easy paced running. Long runs and semi-long runs run off at MP + (at least) 60s and the easy runs at MP + 90secs. One thing that Liz Yelling taught me post Super Six was to keep practicing MP as much as possible so using the longer runs to introduce blocks of 15mins at MP is a good thing especially near the end of the run so you’re learning how to run at MP on tired legs.
Ideal week (for me) if I was planning a schedule would look like:
Mon – 30mins easy run
Tues – max 60mins easy run
Wed – run to club (2 miles), club session (7 miles), 4miles loop home (class this as semi-long run)
Thu – 30mins easy run
Fri – max 60mins easy run
Sat – rest
Sun – long run
I would not do 20mile runs on consecutive weeks, instead I’d do 16 miles one week, 20 the next then back down to 16, etc. This does mean you need 10 weeks to do your 5 longest runs before a 3 week taper. Liz advised your longest run should be 4 weeks out – a 3hr run where distance is not the primary concern. My 22 mile run pre-London 2010 was 3h07mins / 8m30s pace.
Liz totally is against 20mile races in the build-up to a marathon – I did this 5 weeks pre-London 2009 and believed I never really recovered from it as I did it at faster than MP. Even running it at MP is too destructive and never leaves enough time to recover from.
Liz would do her last long run 4 weeks out then 3 weeks out do a 2hr run at MP + 20secs so for a sub 3h15 aspirant you’re looking at roughly 7m50s for 2hrs. 2weeks out do a 90mins run at MP + 60secs and then 1 week out do a 1hr easy run. Don’t make my mistake where I did 4 races in the final 4 weeks of my 2009 schedule, which allied to my 20mile race meant I was too tired for the one race that mattered!