The problem here is 'loitering with intent.' I travel through LHR on a reasonably regular basis (2-3 times per month) and either of the junior members of the Duchess Clan drop or pick up. I have an arrangement that they stay outside the terminal area until I text. I do that approaching passport control so I am always waiting outside for them to pull up. I am reluctant to say it but never been caught yet - in 7 years.... Luton on the other hand...money grabbing b*S*ard5****.
My argument is what's the difference between me doing that and someone dropping off? In my case the car is stationary only long enough for me to throw my hand baggage in the back and jump in myself. I've seen people carriers parked up and take 5-10 minutes to unload so I am definitely causing less of a problem.