The last two times I have flown out of Heathrow airport the exact same thing has happened to me. While queueing to get through the metal detector and have my bags scanned, the fire alarm has gone off and I have been forced to leave the building and wait about half an hour to get the all clear. The friend I travelled with the first time this happened has also reported that it has also happened to him on a separate occasion.
Now, this could be simple coincidence or one of three things is happening:
a) someone is lighting small fires beyond passport control quite regularly
b) BAA has been sold some duff smoke alarms
c) since the smoking ban was introduced in England, a few naughty people have been smoking in the toilets.
If the answer is C (and staff at Heathrow suggested that it might be) then this represents one hell of an overreaction. Quite aside from crying wolf, hundreds of people are inconvenienced, stress levels are raised in an already tense situation and flights are delayed. Before I start calling BAA to find out what on earth is going on, I just wondered if this has happened to anyone else. Have you noticed the fire alarm going off in English airports with any frequency?