The Air Cadet Organisation is currently implementing a new system of basic checks when someone pitches up asking to join the staff. All unit commanders have themselves to provide ID to WHQ, in order for them to be able to verify the the IDs of potential staff.
I presented my 1250, and was told the same as teeteringhead. A 1250 wasn't good enough, and I would have to show my passport. In order to join the ACO I had to undergo DVA and CRB checks, which meant I provided 5 forms of ID in order to get my VR(T) commission and therefore my 1250.
I was also at MoD recently, with a Gp Capt who used to work there, and again our 1250s were not sufficient ID, even though we were booked in for an appointment.
Go figure.