Someone found the blog with this first question.
If my driving test is cancelled, can my instructor still charge for the lesson/car hire?
Unfortunately, there is no law which says your instructor cannot do this (that I’m aware of, anyway). However, if he or she tries it then they are the biggest scumbag in the history or the world, so dump them and find one who isn’t a crook. And make sure you tell your friends so they don’t end up using the same instructor.
If a test is cancelled by DVSA, it is beyond your control. You should not have to pay extra as a result.