For bookers you need to show how you qualify for a wholesale account (business / charity etc) You might be able to use ID to get CostCo membership, they accept civil servants but you have to pay a membership fee
Wholesalers can be less of a saving then you expect depending on what you're after. I use bookers for some things, catering is cheap, but most retail brands are aimed at convenience shops so supermarkets can be cheaper than the wholesale price
Depends on the place and who ever is there at the time . I have a card as I told them I run the unit tea boat. I had to fill in their standard form, name, address etc and name of the company so make something up or put your name in again.
Speak nicely to whoever is on the reception and just try it. Didn't have to show my MOD90.