I wonder what the legal background of this is. My understanding that every work created by the UK government is protected by crown copyright which is only waived in certain very specific cases (and this is not listed amongst those). Can anything under crown copyright really be considered open source? (It doesn't say anywhere that it is, by the way, although there is a BSD-style license).
Pwrhaps ironically, the existing direct gov page has information on permitted uses of crown copyright materials.