Not on Southern. In particular, given 12-car formations couldn't go DOO on the Brighton line until the changes in 2016, which is about the only place 12-455 could operate, although 455s went to Brighton fairly often, there wouldn't have been a lot of motivation to run 12-455 formations at any point. In slam door days, 455s would occasionally run late night services to Brighton DOO when a guard wasn't available.I don't think there has been a 12 car 455 in passenger service in the last 20 years at least.
12-car 455 formations have historically operated on SWR to Basingstoke or Woking from Waterloo during service perturbation or strike timetables.
https://www.railforums.co.uk/thread...tion-into-service.122552/page-70#post-3287020