Here's a bit of polite advice for the management at Sheffield City.
I did a little jaunt up to the Peak District yesterday and thought I'd stop at Sheffield for fuel and food. So I phoned for PPR. I was told that, as I hadn't been there before, I needed to fax them a signed terms and conditions form before they could accept me. I didn't have access to a fax machine at the time and had no burning desire to go there anyway.
So Sherburn got my money.
Its your airport and you can do what you like and the staff were polite about it. But this kind of policy smacks of blind following of conservative legal advice without sufficient thought to the commercial effects on your market. It does not encourage GA to pop by and give you its business; not everyone plans flights much in advance, especially on Sundays.
AFAIK no other GA airport requires this other than for out of hours use. Its not even good law - there are plenty of other ways of effectively imposing an indemnity clause as part of a contract if that's the issue.