This does not sound illegal to me. You were all accepting that the camera was used, it wasn't hidden or anything like that, and you are all old enough to know better, I mean give consent.
Now, what you do with said photos once developed is another mater. Embarrassment is one thing, but blackmail is definitely illegal (hohoho!).
Sending the embarrassing pix to the local (or even National if your friends were famous) papers whilst not illegal in itself, could end up in trouble for you if you did so to make money from private actions that were understood to remain private, and the pictures were taken in a private place (oddly, a Public House is a Private Place). In that case both you and the newspaper might be up for some serious courtroom time if the other people became lawyer happy.
On the other hand it sounds a a whole load of fun and you will fall about in hoots of laughter alternating with cringes when you show the pictures at the forthcoming coffee morning for these genteel friends of yours.