My 2p worth:
Problem with Sheffield is it is very GA unfriendly, and in the absence of regular schedules and charters they can't afford to turn this sort of business away. I am referring to the airport being GA unfriendly, not ATC who I find very helpful and of course professional. With the lack of regular services I would have thought GA traffic would be welcome and might even get the punters in the catchment area to start thinking more about "their" airport.
There is no logical reason for the refusal to allow single engine fixed wing a/c because there is more open ground around the airport than at many other airfields. It is not at all like London City in its location.
Last time I landed at Sheffield there were more fire engines than aircraft and I was charged more than I had been quoted on the telephone the day before. I've not been back since.
Wonder how much business this GA unfriendly stance has cost them over the years?
It seems a great waste and shame.