Everything that decides whether airport parking goes smoothly, in the order you actually need it. Most of this happens at the booking stage, where it costs you ten minutes and nothing else.
Before you compare anything
Confirm your terminal, if the airport has more than one. At Heathrow and Gatwick the car parks are genuinely separate places, miles apart.
It is on your airline booking. Check it again in the week before you fly, because airlines move between terminals more often than passengers expect.
Count the days the car is actually parked. Not your flight dates. A red-eye landing after midnight falls on the next day, and a trip described as a week is frequently eight days once you count both ends.
Choosing the car park
Collecting someone or a brief visit — short stay, which is priced by the hour
One or two nights — a close daily-rate car park, since off-airport has too few days to pay back the transfer
Three nights to a fortnight — official long stay, the sensible benchmark
Over a week, watching cost — off-airport park and ride
Early flight, children, heavy luggage, late return — meet and greet
Match the car park to your departure time and who is travelling, not only to the price. The cheapest option is cheap only if the transfer costs you nothing.
Comparing properly
Compare totals at checkout, fees included, rather than headline daily rates
Divide by the number of days to get the real daily rate
Price one option in each category, not five within the same one
Ask how often the shuttle runs, which matters far more than distance
Ignore the advertised transfer time, which measures only the drive
Checking the operator
Park Mark accreditation — the police-backed security standard, and whether it is current
Recent reviews rather than the lifetime average, since sites change hands
A working phone number, not only an email form
The delay policy — do they ask for a flight number and track it?
The damage reporting window, which is usually short
Getting the booking right
Registration — barriers read plates, so a typo stops you at the entrance
Return date — the costliest error and the easiest to check twice
Flight number — the inbound leg, so delays can be tracked
Flexible rate if the trip is months away or the return might move
Cancellation cover — usually pre-ticked, and usually worse value than a flexible rate
Timing on the day
Work back from your airline's terminal arrival advice and add:
Meet and greet — 10 minutes
Long stay — 25 minutes
Off-airport — 30 to 35 minutes
Add 10 more before 7am, on a summer Saturday, or with young children
Check the route the evening before rather than trusting the satnav on the day. Overnight roadworks are common and a diversion at four in the morning is disorienting.
Before you walk away from the car
Photograph all four sides, in reasonable light
Photograph the odometer and fuel or charge level
Photograph any existing damage, clearly
Photograph the bay number, row and level
Remove valuables, and anything showing your home address
Hand over only the car key where the operator allows it
Leave a scraper in the car between November and March
Planning the return
This is the leg people skip and the one that decides whether the booking was right.
Shuttle frequency drops after about ten at night. If your flight lands late, that alone justifies a shorter transfer even when the departure did not need one.
Ring the operator if you are delayed, particularly for meet and greet where a driver has to be waiting. And check whether a late landing pushes you into an extra charged day.
If something goes wrong
Barrier will not open — use the intercom, do not follow another car through
Lost confirmation — rarely a problem; they can find it by registration or surname
Damage on return — report on site before driving away, get it logged, photograph it
Cannot find the car — the car park office can often locate it from entry records
Car park full despite a booking — note the time, get a staff reference, park elsewhere and keep the receipt
Compare current options for your dates at Birmingham, Bristol, Stansted or wherever you are flying from with this list open, and almost nothing on it will come up.