You learn something new everyday. Does this mean that the allocations will *swap* for the weekend effectively seeing 317s on Stansted Express duties in 8-car formation and 379s on Cambridge duties in 12-car formations?
Yes 2016 Franchise Agreement requires GA to fit SDO beacons at 96 platforms and on 27 x 317 units. Like so many of their commitments, it never happened. Does look like they will need to run a few Stansted diagrams with 317s to release some 379s.