I dont trust people who flash anyway.
the highway code is dead clear on the issue, regardless of "popular belief" being that flashing is to let you out.
I wonder how insurance companies settle "flashing light" based crashes?? the highway code is black and white on the issue so insurance should in theory be the same, ie you pull out or across someone when you should give way and its your fault, regardless of them flashing lights.
or do they take a more grey view that "intent" is more important ie you thought he was letting you go so its a 50/50 fault because the guy flashing you should have thought you might confuse the signal.