I know this isn't illegal per se, but generally it's polite to ask for permission from a private establishment if you want to go there to campaign and leave things behind. Wouldn't you agree?
I wouldn;t say it's impolite, but IME it's also not standard or expected.
I’ve some experience leafletting in Edinburgh, mostly anti-(hard) Brexit, pre and post 2016 referendum. Personally, I wouldn’t sticker on private property and I’ve never left leaflets in a place with a visible “no leafletting” sign (which is common). I’ve likely been in pubs where others in my group were stickering; not so much with Brexit but it was absolutely endemic on “both sides” during the run-up to the 2014 independence referendum.
I’ve never been confronted about leafletting or seen anyone be confronted about leafletting or stickering, although I’m sure in some cases pub staff did quietly remove both. I can’t really imagine being asked to leave a Scottish pub because of this or even being asked about it unless perhaps a staff member walked in while I was fanning out leaflets in plain view - in which case they would likely just say something like “sorry, please take those with you or per our policy we’ll have to throw them away”.
I also think leaving feminist leaflets or stickers in a women’s lav has a history that some people aren’t aware of or acknowledging - think of the “Ask for Angela” campaign, for example, where for a while the stalls in the women’s lavs were considered a safe place to let women know help was available if they were there against their will or wanting to get away from an aggressive man, be it date or husband or stranger, and give them a discreet way to alert the bar staff and ask for help.
Bottom line, though: even if people in the pub had done something illegal and the police were legitimately called and responded, I’d be massively put off by the stuff on social media from the bartender. It’s unprofessional and wildly inappropriate and misogynistic. I hope Greene King/Belhaven respond publicly and robustly once they’ve had a chance to review the situation; I’m still boycotting Wetherspoons so I don’t want to add another pub chain to my “avoid” list, but I absolutely will if they don’t clearly condemn the misogyny.