In BS 8214 2016 none of the diagrams show dot and dab plasterboard as to where the sealing should be - i.e should capping seals be covering the gap in blockwork upto a door lining and brought to the face of the plasterboard closing off the void to the rear of the pasterboard as well? Or if joints to a lining and blockwork are tight, should that joint be opened up to min 5mm to place a capping seal here? 

If the joint between the timber door frame and blockwork wall is so intimate that there's no gap, then there is no linear gap to be sealed. Where there is such a gap it should be sealed using BS 8214 guidance. Intumescent sealant should be present level with the edge of the door frame and face of the wall.