I had to drop a friend off last weekend and duly set up an account with Heathrow Drop off, registered my vehicle number plate and a credit card for auto pay.

Bonus is that so far I have not been charged, and it says that charges should be made to your account within 24hrs. It wasn't like I was tailgating a lorry or drifting sideways through the view of the cameras on the exit from the T3 forecourt. Number plate is fully DVLA legal with no odd printing. At least with auto-pay if the cameras or system is having a snooze one day then you might get lucky.