Looking for ideas re improving attic insulation

Calahonda52

Two fotos attached, one a screen shot of a CCTV screen, the other a normal foot of the same area in an attic. Two storey, 3 bed semi D, 1990 estate build

The CCTV image shows where the insulation is missing from the ceiling plaster board where it meets the wall plate.

Don't know yet if the soffit vents are working but looking for ideas on how to get additional insulation in there and still use the soffit vents.

Access is very difficult from within the attic space.
Access also difficult from outside as the the gutters from the neighbouring house are almost touching the gutters of this house in the side passage.
Thanks

BryanF

Take of the plasterboard internally, install vent cards and insulate, perhaps battening out to increase the depth of the insulation zone, then install vapour control layer tape sealed then install plasterboard.

Otherwise try sliding down vent cards and stuffing insulation in - difficult to achieve continuity

Calahonda52

Thanks Bryan, had not thought of doing it by removing the plasterboard, which will have to come out in the bathroom anyway so thats the difficult corner sorted|