Hi dl56uk
Have you spoken to the garage about this? If so what did they say?
The law states that purchases must be 'fit for purpose' - so if they knowingly sold you a duff car they are in the wrong. It could be that it was just bad timing, the fault was there but they didn't lnow about it and if you approach them in a friendly way they may offer to repair or replace as a gesture of good will.
An MOT cert only verifies that the car is in a roadworthy condition, it does not guarantee that it is not liable to break down etc.