There's a common theme running here.
The passengers on this flight appear to be morons. A large number of the posts in this thread appear to be by people on the same intellectual plain.
Just what exactly do you expect crew to do during a take off roll if a passenger stands up? The sheer ignorance on display here perfectly highlights the kind of attitude these idiots must have had. Thousands of people fly on these aircraft every single day and being bmi, the crew were without question highly trained and amongst the best in the business.
So what would you do if convinced there was a fire in the cabin and the crew were not aware? Sit tight and pray?
Quite simply i'd point it out as soon as was appropriate and let the crew get on with their jobs. You know, the ones they're trained for and are checked on at least twice a year. I might even offer to help. What I would not do (and assuming this report is accurate), having a modicum of intelligence, would be stand up, start shouting about fire and bang on the flight deck door during a take off roll.
Like I said, bloody idiots.