Autocruise 2006 habitation door

brendanne2004

Hi, can anyone tell me what the lock to the right side of the habitation door is for please?  It looks like a large hinge with a keyhole
and has a small barrel type key.  

We've just bought the van but the salesman didn't seem to know what it was for.  Also has anyone had problems with locking the main lock on the door please.

Many thanks ... Brenda