Lived in Stoke for a few years and they have a larger than usual contingent of apes, who also seem to love smashing shit up following England matches.
Anyway, here's the thread about this incident on their message board.
http://oatcakefanzine.proboards.com/index.cgi?board=Potters&action=display&thread=90941
Birmingham and Stoke have a history of this kind of thing - there was some of the worst violence of the 90s when they met at St Andrews in 92 and a Birmingham fan lost an eye after being attacked by the Stoke mob a while back if I remember correctly and there's been tit-for-tat revenge attacks each time they've met since (and indeed there's talk of "revenge" when they play over Christmas on that Stoke board)