Yesterday (Saturday 19th) I took the 1507 service from Lewes to Brighton which is always formed of a 2 car 171 in normal service because it comes from Ashford. However, I had a nice surprise when a 4 car 171 turned up. 4 car 171s are based on the uckfield line and are only used on the East Coastway line during special events despite the 2 car ones frequently being overcrowded. Is there a reason that some 4 car 171s are operating on the east coastway line instead of the usual 2 car ones?