Unlike the US, I doubt you'll find that there are many advertised posts that require an MBA. In fact, there are probably very few of any kind that require an MBA. The airline industry in UK is quite incestuous; it often prefers to promote from within, where your track record is more important than the paper qualifications you hold.
Your best bet is to contact some of the executive recruiting organisations in London (check out the Times, Telegraph and Independent newspapers or their websites) who may deal with the few posts of this nature that do come up.