Well in response to the 'how to' request, it was quite simple looking back. the most important equipment as is always the way with experimental shots was a bit of confidence. This is far easier to come by now that you're not wasting a shot or two off a roll. I asked the museum staff at York if it would be OK to set the tripod to run around the turntable on it's own whilst the demonstration was carried out. They started off with a talk, so i set the camera up on my tripod. I selected the cameras multiple timed exposure mode. I set it to capture 6 frames after the standard 10 second countdown. This meant the camera could happily take several shots whilst riding the turntable. My camera is a Canon EOS 450D to which I attached my Sigma 10-20mm f4-5.6 lens, set at 12mm to fill the frame with the loco on the turntable. I added my mounting ring for Cokins superb P-series filters and slid my brand new linear polariser in and my ND8 to allow me a longer exposure for the blur. The camera was set manually to ISO100, 30sec f/22 and this was the best exposure of the 5 it actually got to take before returning to me.
I must say it is very surreal watching your camera and tripod take off around a 360 degree trip away from you, but at least the ride was smooth (for the photo) and it didn't fall over either. I was quite nervous about when the turntable stopped suddenly. Thnaks also to my Velbon CX640 for providing the suitable stability.
So there you have it, nice and simple! Oh, the last thing was that of course, I travelled 3 hours to get to York, and I only had the one revolution of the turntable to get this right. Always good when things work out for you.