A critical architectural design issue is the means of escape from habitable rooms in the event of a fire; this can be achieved in several ways, not necessarily using a rear door.
Building Control requires all habitable rooms to have a primary, protected means of escape to the exterior of the property. In a bungalow, this is typically achieved via a central hallway giving access to a front door. If all the rooms leading onto a hallway are fire doors providing 30-minute fire resistance, then you do not necessarily need another external door. However, if the hallway is excessively long then Building Control might require another exit door.