The theft occurred on 12th December 2008, in the Holburn Office (London, England) of the Bar Council.
The data contains information about barristers, including:
Names and home addresses, which will probably be of some concern for barristers involved in prosecuting criminals, as that data is now in the hands of criminals (though they may not know that, or have the wherewithal to even access the data). But that will not provide much comfort to the Barristers involved!
Despite the comments by the Bar Coucil about data security theft, the data does not appear to have been secured with encryption, so there is no real security at all.