In the UK people like to race up - or down - the left side of escalators in stores, airports, the Underground or train stations. Somehow, they believe the half a second they shave off their journey by walking up the escalator will get them wherever they are going faster. It won't actually, but indulge them. If you are happy to let the escalator do all the work and prefer to stand patiently in one spot from the bottom to the top, stay on the right, leaving the left side free for passing traffic. Otherwise, you'll see a lot of frowning faces and have to suffer the indignity of people trying push past. City people, in particularly, seem to regard loitering on the left of the escalator akin to shoving in at the front of a line instead of waiting your turn. Probably no one will say anything, but you'll get a lot of grumbles.