Why are most anime dubbed in American English, rather than British English? What is the reason behind most anime being dubbed in American English and not British English? Does the control of a country over the world market have something to do with this?
Because most of the companies that first get the licenses to distribute a series outside Japan in English are based in America.

If we look at three of the biggest ones that I can think of off the top of my head, we have:


Funimation - Headquarters: Flower Mound, Texas, United States
Aniplex of America - Headquarters: Santa Monica, California, United States
Crunchyroll - Headquarters: San Francisco, California, United States


When companies in Anglophone areas outside the U.S., like Manga Entertainment (UK), Madman Entertainment (Australia) and Siren Visual (Australia), get licenses to broadcast outside of America, it would be a waste of money to re-sub/dub the series. This is why when you get DVDs/Bluray from somewhere like Madman, you see company logo animations for all the companies involved, including U.S. companies like Funimation or Aniplex, before the title menu.

Re-subbing might be significantly cheaper since you are replacing words based on how they are spelled (color/colour, meter/metre) but re-dubbing wouldn't be because you have to hire the voice actors/actresses to come in and redo lines. If the original VA's were re-hired then it would be possible to get them to redo certain lines, but if you wanted a UK VA Cast then you would need to redo every scene and this wouldn't be cheap. 

Also one thing to consider is that Japan does have different accents such as the case with Toji who has an Osaka accent which was interpreted to be a New York/Brooklyn accent. If an English-speaking company outside the US was to re-dub they run the risk of ruining this and we know how bitchy we can be when it comes to subs/dubs not being accurate.