I would just phone around and ask, I am not sure there is a specific issue with Japanese cars.
I have a very old Japanese car (a 1989 model) that is very rare and I take it an MG Rover specialist because I trust them and it is a car and at that age, quite a simple one. They do not work on any other car that is similar in terms of age etc but are unfazed by it.
They are not in Hertford though as I have used them for 18 years, long before I moved to Hertford.
There are many good independents in Hertford from what I have heard, I am just being loyal.