So, first things first: how long was the flight? If it was LHR - GLA then I'd say the chap deserves a medal for quaffing that much, but if it's LHR - LAX then I'd say it's a poor show and he needs to up his game a bit!

As for the crew policing his alcohol intake, I would agree with the comment that it isn't their place as long as the passenger isn't actually (or likely to become) aggressive. I am not sure I'd appreciate being told "Mr Geordie 405, I'm sorry but you've had X drinks and we think that's enough so we're cutting you off"

Now of course if the guy was to have drunk the bar dry so there was none left for me, that's another matter again