Sounds phishy to me...
So let me get this right. We have all the Ofcom rules about numbering schemes so that we know what sort of number we're calling, and suffered years of renumbering to make everything fit the plan, and O2 are now assigning geographic numbers to non-geographic equipment? They may dress it up as a call-divert approach, but unless the landline number actually terminates on a landline phone belonging to the user, in a real building, they're simply flouting the numbering scheme rules.
I divert my ofice phone to my cellphone for my convenience, but the number still really belongs to my office. The O2 approach is a con.