Hi Holly,
They are on commission and when times are hard they may have less integrity than usual. They should have asked you to sign the plans to say you had seen them. It might be worth giving Trading Standards a ring as the builder may be in breach of the Property Misdescription Act. This is an interesting read:
Walker Morris UK solicitors, corporate and commercial law firm
Sorry to hear about the proce going down, again this is becoming more common.
Tony