Jaia - I posted a thread about this last year which you might be able to find. Last year I asked Admissions this question and was told that children were not allowed to write on the question paper. If they needed to mark the alphabet for VR questions, they would have to write the alphabet out on a separate piece of paper. This was because question papers used to be reused. They aren't these days, but they haven't got round to changing the rules for administering the tests
If I were you I would give them a ring and check if they've changed things for this year.
Just to confuse things, I believe in Kent you can write on the question papers?