I'd never teach in the UK.
In Vietnam the kids are a lot more eager to learn but in the UK half of them just want to mess around and disrupt the class. Inner city schools are the worst - and easiest to find work in - and you as a teacher are almost helpless because so many of the kids are screwed even before the age of 11.
Plus, the working hours are vastly different. In Vietnam I work around 30hrs per week in total, but in the UK it's closer to 60hrs.
60 hours a week?! That's too much. I always thought teachers have excellent work life balance. You mentioned that you want to get into marketing. I am not sure about the European universities but in the US English/Sociology majors have easier time getting into top MBA programs. GMAT requirement for them is more relaxed. The fact that you worked in a foreign country as a teacher will be seen as something positive as well.