Please please can you report this to DVSA as they are now investigating this issue. The more reports coming in the better chance they will do something. Even if you have the repair done or have since disposed of the car it may still be of help.
More information on my current dealings in this matter can be found on here:
https://www.toyotaownersclub.com/forums/topic/184468-mmt-gearbox-fault-p0810-error-code/
