One question, I have heard that most UK pubs only carry one brand. I hope that is not the case.   I was told that pubs usually are owned by the brewers and they will sell their own brand.

Most pubs in the UK are owned by breweries or by (I don't know what you call them) "property groups" (they don;t brew but own pubs) such as Punch Houses may be managed (employed by the brewery), tenancy or leases (not quite sure on the difference there). I think there is a law requiring a tied pub to have a "guest beer" but the choices can be limited and publicans usualy compelled to buy from within the group. Where I am, in North Norfok, Punch seem to be the biggest player.

We also do have "Free Houses" who don't have these restrictions but they are less common. Free Houses btw often have an advantage over ones that are tied when it comes to pruchasing beer BTW. It may sound odd but lets say you had a tied "Tetley" pub and I had a Free House, you could well find I could buy "your" brew cheaper than you can.