Seems that the basis of the accusations is that they hosted a WPUK meeting at some point. The two people accusing them in this particular case are local councillors. They are now threatening libel action.
Reading the blog it seems that this is a pub I would very much like to go and visit if I am ever in Sheffield.
theharlequinpub.wordpress.com/2019/01/08/false-allegations-of-transphobia/