I gave in, and shelled out to see the John Martin show. (It closes on the 15th-) I enjoyed it, although I still think the prices are too high. I particularly liked the mezzotints, which I wasn't familiar with, and the lively son et lumiere near the end was pretty cool.
I was interested to see that Martin did an album on the character of trees, and that one, in Rchmond Park (?) was locally known as 'Martin's Oak'... might be of interest to
although I doubt if it's survived...