I think the pedal too close scenario is quite likely, but I am at the limit of adjustment on both the seat and the pedals so there's not a lot more I can do. I've taken the cable assembly apart and refitted it, carefully tightening all the locknuts, making sure it's all configured as per John's incredibly useful diagram and I think it's sorted. I have applied some thread lock and I will cobble together a pedal stop this weekend. Thanks for all the advice. Fraser.