Sir C de C,
What happened then?
If you are planning Marathons in consecutive weekends then you need to slow the pace a bit. When I was preparing for London to Brighton in October 2000 I first ran Two Bridges 35miles 26/8 in 6-43-27 then Moray Marathon 3/9 in 4-27-14. Then New Forest Marathon 10/9 in 4-47-21 and finally Battersea Park Marathon 17/9 in 4-17-51. London to Brighton was 1st of October and I just managed to complete it.
. As you can see, of the Marathons the last one was the quickest!
Prior to that I had been running between 4-15 to 4-25 about one a month.