I believe I'm right in saying that the Acting Sqn Ldr business was stopped in 1980.
At this distance, it may just be worth recalling that it was simply one outcome of an AFB decision in 1968, driven by a concern at the time over retention and undermanning. More Sqn Ldr flight commander posts were created on squadrons, and Acting Sqn Ldr also applied to Captains in the Comet fleet - the latter perhaps largely forgotten as the numbers concerned were small and the force was withdrawn from service after the mid-70s Defence Review. But there's no denying that the policy was most visible for some years in the left-hand seats of the VC 10.