I don't deny I owed the money because I was sent an unpaid bill. The important thing is that I didn't know I owed it until I was informed in November. I have had many utility bills since 2010 both for my own house and the rental property and all have been paid on time.
In late 2010 I transferred all utility bills from myself to the tenant. Maybe there was some confusion at British Gas and they just found out now in Nov 2013 that there was an unpaid bill and they contacted me!!