There's a running shop on Longacre, Covent Garden, it might be worth giving them a bell, they do quite a bit of analysis and (for me anyways) videoed my footfall as I ran on a treadmill so they could recommend the appropriate shoes. I been lucky and never had blisters hardly ever from distance running, including some 20 mile + runs, so perhaps yours are due to the shape of your feet, perhaps the arches in the shoes you use are too prominent and therefore rubbing ? anyways just a thought they may be able to help.