In reply to birdman:
There are 2 parts of the bridge that are tested for abseiling use: one over the land, one over the water. Both are marked. If there's another group there you may not have a choice though.
If you don't already have one, you won't have time to get an abseil licence by tomorrow (it's specifically for Millersdale Bridge), so I suggest you have a back up plan.
By the way, do check that your insurance allows you to abseil off manmade structures as many just seem to cover rock.
Look out for amazing crinoids on the limestone steps!