Have passed through 2 different terminals at LHR in recent weeks. At one my carry on was pulled aside for a further check but not at the other. Same things in the carry on. I think what annoy passengers most is the lack of consistency over security. It might also help if the signs were bigger / clearer and better positioned for what needs to be removed ie shoes etc. As for marmite why not put it in checked luggage rather than carry on?