Cant help much other than to say most of these things are sorted by rest. I started this post prior to running my first marathon as I had repeat calf rpoblems and was only 10 weeks from marathon start. I went to see an osteopath on one of the recommends. They were great, identified the problem (it was actually an achilles problem) which may have been caused by a range of things. I was given some very specific exercises and total rest for 5 weeks. I then was allowed 3 runs over three weeks and it got me fit enough to get round the marathon. I continue to follow her advice and have no problems since. The great bit was she did a proper skeletal check and the whole mechanics for me.
Thanks for the advice everyone, completed my first marathon on Sunday in Loch Ness - calf and achilles all fine (most of me fine actually). Managed to avoid think of times but am quite pleased with a 4hr 24m finish considering the build up (and the massive hill at 18.5 miles that wiped out so many people).