Like bednobs said, I also think the photo was of Jo, it didn't show who she was related to, just a cliff hanger. Bet there's a lot of rewinding and screen-shotting going on tonight! I also think Steve referred to it being a he.
I'm guessing it isn't going to be one of the more obvious Scottish ones like Tommy Hunter or the police officer, Philip Osborn played the the lovely Mark Bonnar.
I think the photograph Jo has in her apartment may be a clue (or just another red herring), the woman in the photograph looks a bit like the mother of John Corbett, the one Ted supposedly had a bit of a thing with. Could be partly why they have kept his widow in it and, if Ted has links to her (the money and their meet up where Steve spotted them) then he could get implicated if not involved.