Thanks to all who have responded. This has pretty much given me what I was looking for. A few points to add:
1/. Nitpicker (#3) is quite correct - that's why we are paid (at all - let's leave aside the amount for now....)
2/. Mr Horgy (#9): In the scenario I presented, that would be a "land after the departing" type clearance, which is illegal except where mandated by the CAA. (Can't face looking up the exact reference...) Doubtless Gatwick and Heathrow can do it but I would suspect that the unit MATS2 would stipulate conditions. (Any help GONZO?) Otherwise we'd all put our feet on the desk, say the phrase, be paid the "big bucks" anyway and let the pilot make the hard calls.
3/. Denti (#8):
"And then it was clarified by the company recently that it is legal to continue the approach below minimum if visual conditions are met without having a landing clearance. But a go around should be initiated at 50ft if no landing clearance is received by that point to avoid touching down during the balked landing. Before that we had a lot of go-arounds at minimum even with a warning for late landing clearance."
"Before that" was exactly what I'm talking about, with say a non-precision approach with quite high minimas. It's all going to work - have give the "expect late" bit and departure rolling - but nonetheless too tight for a relaxing life and then the pilot goes around because (despite VMC) he's got to minimas. Say he's at height 500' and only just inside 2 miles out. Should be enough. Given that on a visual approach if unstabilised, a pilot is mandated to go around and the 500' is again just inside the 2nm, I might well be more cautious about issuing "immediate t/o" if the arrival is on a visual. Because you then have the nightmare presented by....
4/. Capn Bloggs in #4:
"Go Around at 200ft to 15-20° nose-up with an aircraft taking off on the same runway just ahead, below and slower/accelerating..."
At that moment - just as you want the departure if not actually airborne or past 80kts - to be instructed to stop,or if airbourne, pass traffic (at least), some vehicle driver calls and blocks the frequency. That is not an easy scenario and should be avoided by prompt action BEFORE it gets there. For an even spicier life, let's say the G/A misses the slow climber but there is a vortex wake issue and the poor unfortunate departure is about to fly right through it.......
5/. So, what would you pilots do in the horrible event that 4/. materialised in front of
you? (You'd have been succoured into a shambolic ATC situation agreed....)
Amicalement,
LISSART