From aa-asterisk.org.uk wiki
The Office of Communications is the independent regulator and competition authority for the UK communications industries, with responsibilities across television, radio, telecommunications and wireless communications services. Among other responsibilities they publish the National Telephone Numbering Plan and the codelist.zip file used by Ofcomverter.
There are a number of errors in the data, some of these are detailed on the National Telephone Numbering Plan page.
There's also a replacement file for the sabc.txt data with these errors corrected and noted.