It was made quite clear to me and my colleagues on our induction course at work (10 years ago now) that social events after work with 3 or more people could be construed as work events, and behaviour there had to meet the standards that would be expected in work
Perhaps I could set "show me the ET or, better, EAT judgement" to music, and do a little dance.
HR training people are very keen on saying things like "could be construed as" without having much evidence that it ever has been. They want to (a) show they're worth their money and (b) imply they know more than you, so they're hardly going to scale down the purported risk.
If your promotion processes are transparent and have properly constituted interview processes, then they will withstand review and tribunals. If you're reduced to waving around policies about who can go to the pub with whom, you've got deeper, more serious problems. If you're only promoting white men, and all you can show is that you discourage white men mixing off the premises, you're fucked.
I think the point is that if it could be demonstrated that promotions were always within the group of pub-goers,
Firstly, they'd have to show that was the case. And secondly, even if it were the case, they'd have to show that due process wasn't being followed. If the employer has properly written records of interviews, with contemporaneous notes and feedback delivered promptly and effectively to the applicants, and the decisions reached are defensible, no ET on earth is going to second-guess them just because people were going to the pub. If on the other hand you only promote white men and have no records of how you do it, the pub is hardly going to be the centre of the case.
If the allegation is raised that a cadre of people are drinking together and promoting together, then you need to be able to defend your promotion process. The way you do that is having a decent promotion process, not by attempting to remove the side-issues of how the cadre meets.