Very curious as to why they would not allow it, even if you are in a tandem seat aircraft, with a thorough briefing you should be able to allow the student to have a look at a few briefed figures. This has never been a problem for me in the Pitts, even people with zero aerobatic time, with height in hand you are so far ahead of them you can always take over if you need to.
Sounds like a busy aerobatic scene there in the UK, exciting stuff.
cheers,