DPOC was Deep Persistent Offensive Capability which had its provenance in FCAC (no idea) and FOAS (Future Offensive Air System).
All GR4 replacements really. A manned/ unmanned mix was talked of at some stage.
Nevertheless, as FB11 points out F35C could meet DPOC criteria where the F35B can't. Hence the saving of (a convenient) £1billion from curtailing DPOC was taken into account in the maths for going to the F35C.
One assumes that we'll need DPOC back if we go back to B...