It was down to Alan Johnson in the poison chalice chair to make the announcement.Some may argue that this was Gordon Brown's way of enacting revenge on a potential competitor.
Mike Smithson writes that
Alan Johnson’s main claim to the leadership, beyond not actually being Gordon Brown, is that he is an honest man of the people. If this announcement is mere political posturing to make him more palatable to the civil liberties Left, whilst not addressing their core concerns, I suspect he will do his ambitions more harm than good.adding that
I think Johnson needs to go further if he wants to gain political capital out of this. Abandoning the Identity Database for UK citizens would score him real points, and by (for example) making it purely a register of non-UK citizens resident in the UK he could paint it as an immigration issue, with the Tories and Lib Dems on what I would expect to be the less popular side.