Maybe you know more about law in the UK than I, but I believe the criminal issue is between HM's Land Registry and the person who sold it, and there is only a civil issue between the rightful owner and anyone.
Criminal law in England and Wales is between the Crown (represented by a prosecutor, often but not always an arm of the state) and the alleged criminal. So the question 'who is the technical victim' isn't usually very interesting. The three salient questions here are:
1) Has the person committed an offence (probably yes: fraud by false representation, contrary to s.2 Fraud Act 2006);
2) Is there a reasonable prospect of conviction? (Who knows: will depend on the evidence); and
3) Is it in the public interest to prosecute? (Almost certainly yes).
'Who has been defrauded' doesn't even matter for establishing (1), only that the fraudster intended to make a gain for himself or a loss for someone else by making a false representation (in this case that he was the owner of the house). So in this case it really is a bit crappy from the police: if a fraud has been committed it doesn't in principle matter who complains about it, they should investigate (or at least register the crime) anyway.
Did you notice who you didn't list there?
The home owner.
The criminal issue doesn't involve him!