They won't allow you to take the test, or if you do, pass after the minimum hours. The point is that the school/ CFI/ FI/aircraft owner have a financial interest in maximising the hours you need.
They may not want you to fail and they definitely don't want you to give-up but the longer you take the more money they make.
I disagree. The School's financial interest is in doing a damn good job so that I come back after the PPL for 50 hours a year solo hire, not in messing me around to try and extend my PPL by 10 hours (after which I get pi$$ed off and leave). The 'fixed'-price PPL-in-3-weeks operations may be the exception here - but this is already the case with the JAA-PPL.