We are booking a minicab to get form LHR to Kilburn on Dec 26. All the companies incl Just Airports indicate that parking charges are extra but no indication of how much extra. We have not used a car service before - we always take Heathrow Connect and cab from Paddington. But on Dec 26 that's not an option.
Anyone have any ideas how the parking charge or any other extra charges works? I am assuming JA tracks your flight in case of delays. Or do they just show up at the flight arrival time and park?
My concern is that I know it'll likely be an hour or so as we have checked luggage etc so we'd like to avoid a service showing up at 2 PM and waiting till 330 and charging us parking and wait time. Some companies let you specify how long after you'd like the car to arrive.

At home we often use Uber/Lyft but it seems more a hassle at LHR.
Thanks for any info.

Topping

We've used Just Airports twice going into town and both times the parking charge was under £10. The second time our flight had been delayed for 3 hours, but they do track the flights so they don't show up and have to stand around all that time.

I want to say the 2nd time was roughly £6 or so if I remember correctly (but definitely under 10) and that the first time when our flight was on schedule it was under £5.

As trophywife says -- you give them the flight #/arrival time and they monitor it in real time.

Normally the parking charge is next to nothing because they don't park until a few minutes before you are expected to exit the luggage hall. If you are delayed a long time in immigration or if your luggage doesn't come out timely - then yes, there could be extra charges. I've never paid more than £5 (but I always travel carry-on-only so never have to wait for bags)

Honestly, I don't think I have ever paid extra for parking charges. I usually pay in cash on arrival. Of course, I might have missed a few £ s but seems like the charge has almost always been what was indicated on website prior to pick up.