Watch a mainline train run along part of the London Underground

There is going to be a chance to see a mainline train travelling along part of the London Underground as part of a special farewell tour for the SWR’s Class 455 trains.
SWR into British Rail (c) ianVisits
Two trains will run the trip on Sunday 21st December, and after leaving Waterloo, they will diverge from the mainline just before Putney to run over the District line tracks to Wimbledon, where they will rejoin the mainline.
That means fans of the unusual can see an SWR-branded train pass