In reply to Boulderdash86:
Haven't used Harveys in this weather but...
I have spent the whole week-end under a mix of horizontal rain, fog and sleet, and have been "scrambling" up wet cloughs around Kinder Scout and I thanked myself for having taken for once my Ortlieb waterproof case. I was utterly wet but my map was happy and dry. I usually don't take it as I don't mind trashing a map but this week-end I would have ended up with a ball of wet paper.
Sorry if that seems obvious and you have reasons to avoid it. (I suppose it's not good if the area you are interested in is larger than the case and you need to refold the map). Not as handy as a Harveys but certainly comparable to the OS waterproof ones (which I find very impractical).
Edited to add: I have used laminated maps in the past and had similar experiences, after a few uses, the folds lose the protection, water goes in and they're ruined (worse than paper because you can't really dry them). Now I either take a normal map that might not survive or the case.
Post edited at 16:37