A month to month lease agreement was signed by my ex finance, who I stayed with, but he has since left and he did not tell the housing company from whom he rented, and I continued to stay there without paying rent. I have now signed a lease agreement with them, but obviously the rental is in arrears. Should I offer to pay the arrears or should I wait and see what they come back at me with?

Be honest and pay them their money. You can't live in a place for free, no matter whose name it was in... you stayed (and knew it wasn't being paid for) he didn't... you pay he doesn't. Just the honest thing to do.

Since you occupied the premises you owe the money. I'm surprised they signed a lease with you while the rent was in arrears.