The reason for that is the number of people who carry a compass with right intention, try to find Qiblah, but have no idea which direction to face.
I have met many people all over the place who have stopped me to ask the direction of the Qiblah using thier own compass.
Alhumdulillah, having to know the direction is an excellent help to any Muslim. So normally, I would just tell them to pray at 119 degrees from North (when in London). When they find the direction and feel satisfied, it brings joy to the heart.
There are plenty of landmarks around the UK that have compasses all over the place, so that helps too.
As mentioned above, it is good to know the angle in which to face, below are some of those angles.
Compiled on 1 Muharram 1415, Dr.Mohibullah N.Durrani 11 June 1994.