Most Munches take place in the evenings but some are gatherings at lunchtimes....and generally those are casual wear...inc jeans. I was refering to those evening munches/socials.

My local "munch" is on the sunday of every month in a pub and starts at 1pm where there are famiies eating their Sunday lunches lol. So the dress attire has to blend in with that venue (they really dont want grannies and kids choking on stuffing balls!!!! LOL)
Another local munch within the area has a really strict dress code. black dress for the men and all out for the women inc nudity if so wished but under no circumstances no jeans or trainers.

As I said before all depends on the venue

ceegee