They're not complaining about the castle.
They're not complaining about landmarks.
They're not complaining about the tours.
They're protecting the brand name: Harry Potter

I think I can see where you misread that part. The article was clearly being biased, arguing that British Tours had the right to do the tour. This however, was not the issue. Sadly, it is easy to jump at companies and point to them as the evil corporations crushing the little guy. But, seriously guys, this is not about that. WB was only asking them to change the name of the tour!!

All British Tours has to do is change the name of the tour and promote the fact Harry Potter was filmed there with the Title. Seriously, it's not that hard!!!

When British Tours used the name Harry Potter locations Tours they were violating copyright law! In order to be able to use the name, they need to make an agreement with WB. Not only is British Tours making profit by stealing the hard-work of JK Rowling and WB, but they are making it seem like WB is supporting their tours (which they are not) as well as engaging in false advertisement.

*** False advertisement would be when a company sells you a product that will dye your hair red (note: they do not say novelty -- novelty means for the entertainment value; which means the product does not have to work). You use the product because you want to dye your hair red. And guess what, they dyed your hair as well as anyone who tried it green. False Advertisement would also be if they say there are no side effects and the users end up with seizures as a side effect. False advertisement is a dishonest way of going into business. It tricks people into believing things that are not true, and increases the chance they will engage in activities that they wouldnt have engaged in. ***

British Tours did not invent/create HP. And I bet they did not have a tour called "Harry Potter location Tours" before HP.

And yes, by client they may be referring to Warner Brothers as well as JK Rowling.