See also http://www.ispreview.co.uk/index.php/2013/12/confusion-alleg...
In a nutshell, some ISPs will effectively hijack publicly routable ranges for internal use if they know that there's no way those addresses will ever be used for real public services. In this case, a UK ISP is re-using the US DoD's 30.0.0.0/8 network. Anecdotally I've heard the inverse is also true (US ISPs use UK MoD ranges).