It's german and you can rent it from most online dvd places. It's been on Film Four a few times.
It's also on ebay for 50p + p&p
http://cgi.ebay.co.uk/HEAD-ON-GEGEN-DIE-WAND-CULT-GERMAN-FILM-SEX-DRAMA_W0QQitemZ120181609832QQihZ002QQcategoryZ2288QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
No it's not me tryoing to sell it