Any time that you see this icon (circled in blue) in the corner of an advertisement, you know that it is placed there by Google AdChoices. RailUK get money from Google for having that ad there, not directly from the companies which are advertising through AdChoices.
It can actually be useful at times. This one for CyclingDeal.com.au is what's at the top of this forum thread as I view it now. I've bought stuff from them in the past, but I first heard of them because their ads got served to me by Google after I'd been looking around on a few competing online cycling stores. I had a look, and for the stuff I wanted they turned out to be better than the places I was looking, and for a bonus they're Australian owned and operated instead of my money going offshore.