Hi,
I think you may need two different boxes, even if you are in an area that can receive both Saoirview and Freeview Terrestrial signals.
Saorview uses DVB-T, whilst Freeview HD uses DVB-T2, as I understand it. I don't think the Saoirview boxes are built to receive the UK code format - or at least they weren't, in the early days. That's why people started getting combo boxes with a satellite tuner and Saoirview tuner combined, for picking up the free to air UK channels. They do need a satellite dish, not just a Terrestrial antenna though.
Perhaps things have moved on now though....