Hi SMT
As Somerled stated, first thing get a solicitor to work on your case and put all the info like dates and amounts you invested, property addresses, tenants names and rents paid all onto a few sheets of paper.
Next if you haven't got bank statements to prove the movement of monies in and out of your account referring to the time of receiving the inheritance and the time you transferred the money towards the house purchases, then I suggest you get these as soon as possible and keep the originals sent by the bank. Also if you have a copy of the solicitor's letter referring to your inheritance this could also be useful.
The more evidence you can gather then the better your case should be but make sure that you get a solicitor who has experience of this sort of case. I cannot see why mortgage fraud would come into this, maybe a repossession of the properties and your solicitor should be able to keep you in the clear even if a case was brought against your ex partner
Somerled Hi, how are you doing? and how is the trading working out for you - Gold to head north after October/November me thinks....