As I understand it you are expected to contact the nominated frequency and/or telephone number from the AIP (also listed in e.g. the bottom LH corner of charts, or the UK VFR Flight guide) and find out if it is active, and if it is, you must route around it. Only those DAs with a nominated Danger Area Crossing Service frequency can be crossed while active - the DACS frequency can issue a clearance. So DAAIS-only DAs are out of bounds when active.
But if Plymouth Ops are the nominated body (I don't have a chart to hand!) and they say it is inactive, you can cross. You have complied with the requirement to find out if the DA is active.
Tim