I've now spray undercoated the Mark IV. As I did it outside in the dark I need to touch up a few little bits which the paint missed in good light and then it will be ready for painting. I still have to undercoat the beam for the rear (stern? they are His Majesty's Land Ships after all!).
The tank now sits properly as I weighted the inside with a stack of steel washers.
Gamburd commented on my previous post that the battle around Fontaine during the Cambrai offensive in November 1917 would make a good scenario. This is very true. I am attracted to the Cambrai assault as the British troops were largely Highlanders and these would make interesting looking infantry (and no tartan to paint, thank goodness, as the kilts had a khaki cover). The only problem with depicting Fontaine is that many of the British tanks were destroyeded by lorry mounted German light anti-aircraft guns and I have no idea how I would model this accurately!