Rob Dyer of the BMC has published the following:
"Following a review of anchors used on Southern Sandstone, the way we use bolted anchors in the area is changing. The current system of a main bolt (which takes all of the load), secured to a backup bolt with a swaged steel cable has been used on Southern Sandstone for 30 years or more. However, updated expert advice has recommended that this changes to both bolts equalised to a central point, in line with standard practice elsewhere.
It is not possible to equalise the bolts with in situ equipment in a way that is both strong and will not cause damage to the rock so climbers will now need to equalise both bolts as part of their top-rope setup. In the short term, all swaged wire backups will be removed from bolted sandstone anchors as soon as possible. Additional bolts will be placed where needed at Harrison’s and Stone Farm Rocks as part of an ongoing BMC program of renewing and updating bolted anchors.
Visitors should arrive with equipment to allow them to equalise the double bolt anchors to a central point – there are many ways of doing this but the most common and easiest is to use either a sling or rigging rope with screw gates on each bolt. Remember to extend the anchor point sufficiently to prevent your climbing rope from wearing the rock. It’s a good idea to use rope protectors over any rigging to prevent damage to slings/ropes and the rock from normal movement whilst belaying.
Top Photo: one example of how to set up and equalised top rope anchor on two bolts with a sling. Note that here the sling is long enough that the central point hangs over the edge, which is essential to prevent wear from the moving climbing rope. In some cases, you will need to extend the central point to ensure it hangs over the edge of the crag, (as in the photo to the right).
The BMC would like to thank and acknowledge DMM for their assistance with testing."
https://www.thebmc.co.uk/changes-to-southern-sandstone-bolted-anchors
UKC form post here.