I have been refused entry to a bar, because the management have a policy on people wearing clothing made by this manufacturer. The clothing is clean, non offensive and in my case, brand new. Can they refuse entry simply based on the manufacturer of the clothing? Is this discrimination or a breach of my civil and human rights?
Management can refuse entry to the premises for any reason they choose and don't have to give you a reason, you'll see a sign in the majority of places that states so
If you're talking about England/Wales yes they can, and if you get in they can insist you leave at any time. It would only be unlawful if the clothing in question is peculiar to a separate race, religion etc.
A public house is a house open to the public - there still may be rules to follow, and indeed few people question the age limit. A "free" house is one not tied to a particluar brewery, it's not a reflection on it's door policy or beer prices!
Look at it from the publican's point of view: if (say) a gang in town, known for random violence/bad behaviour/general lawlessness took to wearing top hats, tails and monocles, it would be a sensible precaution to ban such attire from his establishment.
Any bar/club/pub can refuse entry on appearance. It is mainly a city thing I have found. The only thing they can't do is refuse you because of origin/ethnicity.