Do you mind changing your plans? I guess that's a toughie as it could go either way. If you say yes then negatively that shows you can be indecisive, but positively it shows that you are flexible with where and when you work for NATS, and it shows that you can tell pilots alternative routes if a situation arises, so I would guess this would be the answer they would want. But then I didn't even get past stage one so what do I know!
Any other questions that stumped you?
By the way RO13ERTS thanks for the recommendations of books, I've already got two of them on order, I'll get the big fat ATC one when I've looked through the others. Thanks again.