My er spaniel is 8 months old and when off the lead she will not come back even if enticed by treat.?

Hmm...similar thing happened to my dog. What you need to do is make the dog understand that without you, it will have nothing. I would say not to worry now. It's still only a puppy. Try to walk a bit slow, if the dog looks back at you or stops, it knows you're in control and it won't run unless you permit it. Hope This helps !! ~_~