An absurd hairstyle upswept covering heads of Brits and Europeans before the war (10)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

AN + ( MULLET [defined by Chambers as a hairstyle that is short at the front, long at the back, and ridiculous all round ; absurd hairstyle] reversed [upswept; down entry] and containing [covering] BE [ first letters of {heads of} each of B RITS and E UROPEANS)