Just an update on this.
Touch wood - Problem seems to be over for now. Cleaned up the dizzy cap & rotor arm contacts, have replacement ones on order and also cleaned up the ignition switch. Had problems with that a year ago being gunked up and recently it was needing the key turning slightly more than 2nd position to get the lights/dash to come on, and had no issues since then. I will try and replace that if possible, the contacts inside look worn.
But a part of me still thinks it could have been the fuel seeing as it started almost as soon as I used E10, and now it's just diluted/run through? Maybe I'll never know, but won't be using E10 again anytime soon. I also don't think a problem with the ignition switch would be affected by giving it gas when trying to start?