UK Landlord Forum / Life

My son and 2 of his mates rented a house whilst a Uni but moved out in June after telling the landlord that they where not re-newing the agreement.  BUT the boys had signed a copy of the agreement NOT the original and not given it the landlord.  The landlord has found this signed copy on top of one of the boys wardrobes whilst tidying the house and is now saying that as they have signed it they must stay in the house for the next year.  As it was only a copy, is this a legal copy.