I don't think that we can shed much light on your issue. The North American version of the Fiesta has many detail differences. Especially when it comes to the electrical systems. If we had any specific insight here, someone would certainly share it!
One question. Aren't the Fiesta enthusiast forums in the U.K. responsive to these kinds of questions? This site is aimed at the North American version of the Fiesta, yet, we get quite a few visitors from the U.K. and other places! The Ford Fiesta fan base in America is not large. We are almost considered to be a "sub set of a niche group" in the whole spectrum of the car enthusiast universe here in the states.