There has been talk of making nice membership cards for chapter members, but the cost was deemed prohibitive. If we were making nice accreditation cards at the same time there would be economies of scale and the idea might be feasible.
I think accreditation of photographers is something to be discussed on commons. If commons implements such a system, WMUK could get involved to the extent of issuing cards, but I don't think the chapter would do much else.
The risks to the WMF from being involved in the process also apply to WMUK, although perhaps to a lesser extent since we don't host the sites. I don't think printing the cards would be a problem, though, as long as the design doesn't say "Wikimedia UK" on it anywhere (except possibly in small writing on the back saying "Card produced by...").