The book I am referring to is entitled Criminal Law by Law Express written by Emily finch and Stefan Fafinski it costs £10.99 and I got mine from Waterstones.
Here is the first paragraph in the introduction (this book is an exam crammer for degree students)
Criminal law is one of the core subjects for a qualifying law degree so is a compulsory component on most undergraduate law programmes. Aspects of criminal law also appear in other subject such as environmnetal law, family law and company law, as well as relating more directly t the study of criminal justice, evidence and criminology. As such, a thorough understanding of criminal law is vital for law students.
FAMILY LAW - fraud is actually more prevailent in family in my belief than most branches of law.
Here is the first paragraph in the section in that book on the subject of Fraud
The Fraud Act 2006 simplified the way that the law applied to deceptive behaviour
Under the old law, the focus was on the consequences of the defendent''s behaviour, i.e. what he obtained as a consequence of his deception. If the defendent did not manage to deceive anyone or he did not obtain anything as a result of his deception, he would not incur criminal liability. The Fraud Act 2006 is based on the Law Commission Report on Fraud (Law Com No 276).
I would point out at this time that the contact the tennents have with your wife is nul and void as she had no right - in legal terms jurisdiction or power, to enter into a contract to rent out the house to a third party with or without your permission.
Also I believe that the bank under the circumstance would be very hard pressed to terminate your agreement with the bank when it is not you who has gone out to breech the terms of the contract you have with them.
A case in point is Eteridge v The Bank of Scotland which was a case in family proceedings. In that case the house was awarded to the wife and the husband was supposed to pay the mortgage. The husband went fraudulently bankrupt and the bank went to repossess the house. The court adjudicated that the bank could not repossess because the house was awarded in good faith to the wife and it was the husband who had not only breeched the court order but committed fraud (not just against the bank and his ex wife but presumably against other ligitimate creditors whom he had defrauded in a fraudulent bankruptcy).