You have to go through CRB checks before you can do lectures to cadets. If you're lucky, they might rush it through in about 6 months.
A touch unfair
Chevvers. It's more like 6-8 weeks in my neck of the woods, 10 if you're very unlucky.
And the DBS (as we are reminded below it is now called!) is only required for "regular unsupervised access" so a temporary visitor could be "chaperoned" - and of course now that 18+ cadets must be DBS'd, those cadets could be the chaperone (or chaperon).