Is fraudulent signing as someone else for loan against a property illegal?

[suzcherkin]

I bought a house with my (now ex) partner, we are both on the mortgage & both on the deeds. I had to leave him and the house due to his violence, and we have never resolved the property (him buying me out etc), a good few years later he contacted me asking me to sign a document to allow him to take a loan out against the house, I refused. I have just found out that he has since taken two loans against the property without my knowledge / consent / authorisation / signature, they were for £30,000 for 15 years & £20,000 for 8 years, which means I am liable for half of £50,000. I found out when I went into my local branch to ask for a balance which is required by my solicitor as I am now trying to get the property sold through the courts. I have asked them to forward all the relevant documentation to me. They also confirmed that they would have needed my signature to have authorised these loans. Questions, Is this a criminal offence? Will the building society automatically prosecute him? What is the penalty? What should I do next?

[VHG]

Triplicate append - Law, Civil and Criminal sections