A few years ago there used to be a Redhill - Victoria service in the early hours formed 4/455. I suspect this one does something similar.
Redhill drivers (in a certain link, I don't know exactly which) sign 16x traction and the entire route between Redhill and Reading - both the Southern Region platforms and the main station. There's a handful of GWR services they work - generally towards beginning and end of day. Post privatisation Redhill lost its work to Reading, and all N Downs services were worked by Reading drivers - the first trains off the sidings worked by drivers who taxied from Reading. Then a few years ago one of the very early Reading blocks (2010?) saw no access to Reading for Turbos on the North Downs, so they were route cleared for and serviced at Selhurst for a couple of weeks. This required SN drivers, so they went the whole hog to reduce taxi costs and keep useful traction knowledge in case it's required again and trained them on the road to Reading.