Have you tried threading pedal in from the rear?

Three summers ago I had a pedal loosen on a (funny coincidence?) UK made Raleigh GP and before I got home it was twisting in the crank.

Wrench at co-op threaded the pedal in from the back side of the crank, then screwed in as normal from front. Worked fine though I always wondered about it.

Last year my son took that Raleigh over and this spring sane pedal loosened again but this time I replaced the cranks because it was too far gone. I believe it might have been salvageable again if he'd noticed in time.