The right time for exam marking honesty?

Normally one has to endure the spectacle of aged commentators raining on the parade of cheerful GCSE and A level students as they get their exam results in August. But it is quite something when an exam boss chooses a time when students are nervously sitting their exams to tell them that the marking might not be up to scratch. Of course, complete consistency in marking essays is impossible; and it is right that students should be aware of the fact. But is this really the right moment for the new head of Ofqual, Kathleen Tattersall to share this insight?