I'm usually a jinx when it comes to the sleeper - but last Wednesday night I made it from Paddington to Penzance without incident. The train was hauled by 57303 which failed on the blocks at Paddington last night. Three days before I travelled I saw the same loco on the nuclear flask train heading north - although it had another 57 with it. I think that is standard procedure in case of failure given that you don't really need two locos to haul two wagons.
Where was the flask train because 57303 has been solidly working the Sleepers for weeks now and should have been nowhere except between Paddington and Penzance.
I suspect you could have been mistaken.
57303 is on long term lone to
FGW▸ to cover for there 57's.
As for there being 2 loco's on the flasks
NR» want 2 on each train due to the nature of the load in case of problems.