A few months ago I was crossing the road at Finsbury Park early in the morning and the steam train went over the bridge. I couldn't see it but I heard it and there was a great plume of smoke (steam?). The elderly gentleman stood next to me, slightly the worst for drink even at that hour, asked me if I though it could be a dragon. I told him that I though it probably was and we both walked off smiling.
I thought the Sir Nigel Gresley had been repainted in BR Blue but maybe I'm out of date. If it's Tornado then it's well worth a look. Incidentally, the 7:15 start has changed to 8:18 passing Finsbury Park at 8:27 on the way to York and passing Ally Pally on the way back at 21:14.