I saw it at Retford leaving platform 1. I don't know whether or not there is a bank, but I have seen several steam locos at Retford before including Bittern (the loco that Dominion of New Zealand until recently being renamed/ repainted), Sir Nigel Gresley, Tornado, Oliver Cromwell and Princess Elizabeth. Most of the time, they don't even have a diesel on the rear (and either use steam heat or a generator coach) and they always seem to be fine. It is strange that it appears to be having assistance.
There are some videos of it on You Tube (I have seen one of it leaving Retford and another at Hadley Wood) and you can hear the diesel revving.