Load of clubs in the SE run M chassis classes, Eastbourne, West Kent (tonbridge wells), Capel (east kent somewher) and I expect more of them, West London perhaps, lots have mixed Tamiya classes as well. Adur maybe run them
I think Eastbourne/WK/Capel all run to same rules, one class with silver can and limited mods then a brushless class
https://www.eecc.co.uk/classes/tamiya-m-chassis/ they are all on Facebook
Other clubs like my local up north use torque tuned. There is no BRCA m chassis class unfortunately
Have a look through here for clubs with names you recognise from your area and look at their results, see if any run tamiya/mchassis then look for them on facebook etc
http://rc-results.com/viewer/