Warhead fills in the missing hours of Sergeant Michael ‘Psycho’ Sykes, the least vapid and most outrageously stereotypical of the first game’s heroes, deployed elsewhere for much of its plot. “I’m English, you Muppet!” we’re reminded twice, without provocation, as both alien invaders and the North Korean army are given a five-hour bout of top-class GBH (Great British Hassle).