You are in breach of your contract if you are obliged to tell them that you are renting the property. Is this not tantamount to fraud?
Well a court would have to decide if not telling them it was now a rental is fraud, and I cannot see a court looking favourable on an ordinary person saying I 'forgot' to inform them about this fact. With financial climate of the last few years a change of interest rates would see people over the edge even further, my advice is in that vain.
Is it 'fraud' for banks not to inform people that they are entitled to trackers when fixed period ends?
In any case I don't see a bank taking someone to court to prove this 'fraud.'