Clanger - imagine a test candidate who has been waiting for a test for over a week due bad weather, has the I/R course booked to start next Monday, is rapidly running out of money as they pay an extra however many pounds or dollars on hotels/rental cars/food away.
Imagine a candidate who has managed to get three weeks off work and not a day longer or they will be dismissed.
Imagine a candidate who has a last chance airline ticket from wherever the flight school is back to home/family/work...whatever.
If the good cheese holes all line up and allow them to do the flight test. Not a breath of wind. CAVOK day. Aircraft booked in for maintenance later in the afternoon - will ground it for the next three days.
Candidate checks brakes and they work. Perfect for single crew operations.
Examiner checks brakes and they don't work.........go or don't go?
As for integrated courses - the "progress test" is done by an in-house examiner who knows that the student will have further training before the course ends, the school has areputation to keep, and nobody really monitors anyway - so some will be allowed to go through on the understanding that they will be OK by the time they go to the CAA.
The CAA also say that the progress test is not a licensing skill test as the candidate receives no licence upon successful completion of that particular test...........which is, of course, a load of horse poo - but that's how the CAA work.