Old Sarum sounds fine.
Otherwise, please not too near London.
A pilot was not long ago killed doing aero training under the London TMA, needing to do it between 500' and 2400'. No possibility of recovery from an error at that height, he got into an inverted spin. See the AAIB report. Surely even where the base of the TMA is 3500' its not responsible for aeros training, especially with so much traffic skirting the CTR.