BMI aren't unusual in banning trousers (for female CC, that is...) - in my experience there are only a handful of OK airlines that allow them (sleazyJet and BA are the only ones that come to mind right now).
When I started out as cabin crew (1994) I don't think there was a single airline that let girls wear trousers.
AFAIK sleazy was first, then BA about 3 years ago.
At the airline I work for we have to wear skirts and sheer tights - no chance of opaques even. A while back a few staff tried to get the rule changed but the management said they had researched different styles of uniform with the pax and they preferred a jacket and skirt.
IMHO the airlines that let women wear trousers are putting the preferences of their staff before those of their customers, which is not a good way to run a business. I know of at least one airline (MON) where skirts are compulsory at assessment days - any girls who turn up in trousers get sent home.
I *like* to look smart and be respected by the pax and if the price of that is chilly legs a few months of the year then so be it. You hardly notice if after a while anyway (she keeps telling herself)
