I carried JC on the jump seat once in the mid 70's, returning from a conference, and he said the only thing he would have, in retrospect, changed on the Trident was to have the droop and flap on the same lever, with the last 'flap' setting being the droop. IIRC this was echoed in later editions of Handling the Big Jets by DPD.
After PI, there was a mechanical interlock put on the levers, so the droop lever couldn't be moved without the flap lever in the up position.
During the course of this flight, he said that HS couldn't get to the bottom of why the T3 usually gave a firmer landing, and was more difficult to grease on, than the T1/2. Even he said he couldn't guarantee the landing on a T3. Their best guess was that it was to do with the different 'rigger's angle of incidence' ie the way the wings were fixed relative to the fuselage, and the different height above the ground that that put the trailing edge of the flaps. The theory was, that this distance, on the T3, was so critical, that mm's meant the air being 'sucked' out with a venturi effect (firm) or not (greaser).
bp
.... the deficiencies in BEA
Which were?