They do sometimes shunt sleepers at Wembley. On 25th Oct I was at Stonebridge Park station at around 13.00, and saw 92043 shunting sleepers, adding 15333 to a rake that already included 15004, 15101, 15201, 15307, 15304, 15308, 15307, 15007, 15330, 15331, 15332, 15314, 15304, 15303 and 15305 ( not necessarily in that order, seen as was shunted to and fro).
