I think that they are from the
Shropshire Shufflers. From someone I know who is a member, many runners find it motivational to be part of an organised group - it can be very easy to avoid exercise this time of year if you don't have someone pushing you. They do a lot of their running in the Quarry, but do choose different places, so as to keep up the interest.
In the summer, when there is more light and the ground is drier, they run in the countryside a lot more, but in the winter there aren't many good places to run in the dark evenings, other than the streets.