the fail standard for discs on an mot is VERY minimal,they have to be in danger of cracking in half or similar.service and mot standards are very different,we don’t measure discs on an mot,we aint allowed to dismantle the car so in most cases it wouldn’t be practical even if we did.repairs on the other hand are carried out to different standards,as a for instance new pads on old/worn discs can give brake readings that would fail a retest so you could be in a position where a repair has caused a failure even if the components concerned would individually pass,another for instance would be if the brakes failed on binding,once rectified a faulty wheel bearing(for instance)could be revealed leading to a failure that didn’t originally exist because it couldn’t have been checked in its original condition.having said that its rare and normally at that level the discs should at the very least be useable unless one side was severely worn although no one can be certain from the other end of the internet!the best guess I can give with the info you’ve given is that they have recommended a best practice repair where you have wanted/asked about the cheapest option and that is beyond the remit of an mot and between yourself and the garage concerned.not the first time ive heard similar tho…lastly the mot manual and regs are available as an online resource at gov.uk.take a look,you might be surprised……
