An 'access-only' road or street is that has a ban on motor traffic using it, except for access. Typically this signed with Diagram 620 'Except for Access' in conjunction with Diagram 619, 'motor vehicles prohibited'. The intention is to allow cycles (and people walking) to use the road as a through-route, while limiting motor traffic to just those vehicles accessing properties.
This can be a useful way of creating safe and attractive cycle provision in rural areas; however it may require enforcement.
Image courtesy of MaidstoneOnBike