In reply to ClimberEd:
I ran 2018 and it was very hot on the day (mid to high 20's) and lots of people appeared to be struggling. The spring leading up to it was also pretty cold and/or wet, so no chance to acclimatise to running in the heat.
I was half an hour slower than the time I'd trained for (Longest training run was 22 miles at my expected marathon pace, so was fairly confident I could do it as planned), and it was definitely as a result of the heat and dehydration. I felt awful from the half way point onward and cramped 3 or 4 times in last 10k.
It was my first marathon so I've nothing to compare it too, but other London vets I spoke to after also said it was hard compared to previous years.
There seemed to be alot of people being treated in the last 5 miles or so, and very busy medical tent at the finish line. Again, I don't have anything to compare it to, but it struck me that the heat was responsible.
Post edited at 10:08