well if they do your screwed basically.
I always write my numbers on each page at the very end, after the guy says 'pens down'. Such a waste of time and distraction from my train of thought to write it in the middle of a question. So yeah.. I'll be sitting there scribbling it on each page real quick, takes a few mins sometimes and I'd be the last one out, hehe.
One time the lady told me I didn't have to do it, but I basically told her to feck off as I wasn't taking any risks. 'It's ok, you dont need to do that, I'll take it [reaching for paper]' ... 'I am writting my number on every page' buts in 'you dont...' I but back in 'just incase, you never know...' .. 'mmmk.... mmkkk....' then does that shuffle kind of examiner walk (like on that Chrunchie Nut ad...).