[carpon]

Had the same sort of problem in my kitchen on the rear wall (which is an external wall). The D.P.C. was supposed to have been done six months prior to me moving in(8 years ago) but has now failed. Surprise,surprise, the firm which put in the D.P.C. has since gone bust (or changed it's name) and the guarentee isn't worth paper it's printed on.
Had someone in to look at it (surveyor) who said it wasn't much of a problem, but something that would need attention if I was going to sell.As I'm also a little financially bereft at the moment,He also said it wouldn't pose too many problems if I left it twelve months or so.I try and keep the room well ventilated as condensation also plays a part.
But if you're gonna get the D.P.C. done i'd suggest shopping around and getting a few quotes,ask friends if they've any recommendations 'cause there's quite a few cowboys knocking around in the building trade.