Dropping off the 2-6-2T No 6155. There is another photo of the pair on the Capitals United Express train arriving at the station.Peter Kerslake says I don't quite understand what's going on here as the Cardiff to Paddington Capitals United Express, the 8 a.m. from Cardiff seems to have lost its motive power with an apparently Ex Works 70016 Ariel, looking well turned out as was customary for a Canton engine and complete with Reporting Number, Headboard and Express Passenger lamps all still in place is coupled up to a Tank Engine here at Swindon, an unscheduled stop en route!Hazarding a guess, I would suggest that Ariel is in trouble, and has come off its train in order to take the Tank engine as a helper onwards to Paddington, and in order to comply with Regulations, the Tank is accordingly being coupled inside the Britannia as the use of a non bogie engine as a pilot was frowned upon by those in authority .The driver of an engine in trouble coming up from South Wales would endeavour to get to Swindon where hopefully some alternative or assisting engine would be available, even if it was just a Tank engineIt sems, however, that I may possibly be wrong because the other image of these two this day here at Swindon apparently shows them actually arriving here with the Tank Engine correctly stabled inside Ariel, so, for some reason the Capitals United is double headed, and the load certainly looks formidable .All a bit unusual !!