Looks like the T&Cs have changed since I did a successful run last year. I can’t remember the UK resident requirement (although if it’s enforced I can always change my address back to the UK on my BAEC profile as I’m British so no entry issues).

The other thing the rules seemed to have changed is you can’t leave the UK twice in the same trip but when I did my run I ended it with LHR-HEL-MAN which of course is an entirely normal way to get between London and Manchester. So it seems that’s no longer allowed.

So I think the key points are to always check for changes before booking and also save a copy of the T&Cs in force when you booked in case of issues later.