Well, there are different airport scanners operating at different power at different times for different bags, which are scanned at different rates. You can't really apply other people's experiences to your own situation with a high degree of confidence. If you must carry film on rather than have it shipped to the location, then the safest thing is to have your film hand checked. Period.
Having said that... what happened happened, and you are probably totally fine for a few scans on 400 speed film unless it goes into checked luggage. I probably would have relented for 400 film too if the operator was uncooperative, no worries. But note that if the film goes into checked luggage then all bets are off.
So I certainly wouldn't chuck the film out. But I also wouldn't rely on it for a money shot until testing it. I have a pile of these "suspect" films that I use for not-so-important things like duping or whatever, and so far haven't seen any fogging that could definitely be attributed to carry-on scanners.
Next time, if it makes you feel better, tell the operator that the film is to be push processed at 1600 and they probably won't scan it (at least that's true for TSA in the States). And actually, Ian, last time through National in DC, I was told that 400 speed film was on the boundary of what should be hand checked. They were not insistent either way (and never have been, in my experience), and I had presorted my film into clear bags of <400 and >=400, with all rolls removed from boxes, and it was smooth and quick. I offered to unpack the sheet film but they didn't bother. They sniff-checked the >=400 and I let the <400 go through the scanner.
