I agree...most do. But they have to be inspected by the MoT, so some garages have them out of operation for a while if they are found not to be up to standard. This is especially true for main dealers as they make more money from servicing than they do MOT's, so they aren't too bothered about their MOT stations being unoperational for a month or two.....(that's my opinion from working in a main dealer anyway
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I think you should always get your MOT done as cheaply as possible in my opinion....especially if you have your servicing done at the main dealer, as they should pick up on any obvious problems on their inspection.
Saying that though, I definitely agree that you should get your first MOT done before your warranty expires if you can.....