Localiser
Definately not laser beams.
For starters laser beams light upwards, whilst these 'spotlights' shone downwards.
Secondly they were visible (peridically once at a time) all the way from Milton Keynes down to the South Coast, always abeam our position in line with the moon, so surely not being emmited from a specific ground location.
There is nothing extraterrestrial about it, but probably a natural phenomena which occurs every time there are set requirements present.