Originally Posted by
alanR
The reason for "one bag" is that they are trying to increase throughput through security. Airports like Heathrow don't have a lot of space going spare and installing extra security points would cause (even more) chaos. Of course it doesn't answer why they don't have all the existing points open at all times
So the answer is that they're cheapskates; they won't provide capacity and instead force a reduction in throughput. This is what the insane UK airfare taxes are paying for?