my company operates daily to gibralta. the alternate airfield for political reasons cannot be spannish, and thus nearest other airfield is tangiers. (due to max landing weight restrictions on some a/c we cannot load sufficient fuel for fao.
we even have credit facilities, carry various fuel carnets and all captains have a virtually limitless credit card. on at least five of diverting there, all these have been denied. captains luckily also carry a supply of american express $usd and £gbp travellers cheques. however even these have been frowned upon in the past. unless you are a planned operator into tng with credit facilities, it can be a nightmare.
ps guarantees of payment by fax from ops were also declined.