Garage should collect the car at their expense and provide wheels for you too.
Three times!! Now that would sound good in court - for you.
It depends what type of warranty was issued with the repair, IE Basic warranty, limited warranty, full warranty ETC.
I would consult the paperwork that came with the repair.
If there was no paperwork, i would assume its a basic warranty meaning if the unit fails, they will cover the cost of repair but nothing else.
He now says he needs to replace the gearbox ( under warranty ) as its been repaired twice already and is willing to do this but not until the new year.
If you have a basic warranty, then he is doing what is required and trading standards wont be interested as he has not breached the warranty agreement.
Im sorry its not good News