The DCA has clarified its licensing terms for the SLD, confirming that it is indeed free for all as published. Its Copyright Notice has been amended and the SLD has been removed from the OPSI examples of Value Added Material.
As well as being free “for non-commercial research, private study or internal circulation within your organisation” with an acknowledgment but without any further licence, you are also free to reuse the material for other purposes, “for example in commercial information products and services”, with a Click-Use PSI Licence (apply on OPSI and see the Terms).
The DCA also explicitly “encourages users to establish hypertext links to this website”.
The Department is still investigating the commercial opportunities from providing alternative/additional services.