I know during my time at NCTI we used to teach the studes (mil) the process of anticipation, ie to issue a landing clearance in anticipation of the runway being safely available when the aircraft touched down. I can't remember of the exact distances involved but I am pretty sure that the aircraft already on the runway had to be a certain distance up the runway. So in theory it is cleared to land with one on well up.
At my last airfield we used to be able to land a similar type, stn-based ac with one on (landing) provided that the "one on" was already in the last third of the runway when the clearance was issued . I tried in vain to get the rules expanded to allow a clearance to "land one on" (and only land) with one rolling or getting airborne provided that aircraft was also in the last third but I was told to shut up and forget it as it would never be approved. I personally don't see any problems with it as it is no less safe than landing behind a landing aircraft (especially since the rolling/departing aircraft ahead will always have a greater speed by that point of the runway). Comments please.