Parking is charged per vehicle, not per person — so one car carrying five people costs the same as one carrying one. That single fact decides most group travel questions before anyone asks them.
The constraint is rarely money. It is luggage, and it is worth being honest about that before squeezing everyone into one car at four in the morning.
Is one car always cheaper?
Always on parking, and usually on fuel too. Two cars means two bookings, two sets of booking fees and two sets of running costs.
Where it stops being obvious is comfort. Five adults with hold luggage do not fit in most cars, and a group that crams in to save a parking charge generally regrets it before they reach the motorway.
A sensible middle option people forget: one car plus a taxi for the overflow. On a longer trip that can beat a second parking booking outright, particularly if the extra passengers live near the airport.
Every person you fit into one car is a person you are not paying to park. Every person you cram in is a person who will remember it.
Can one booking cover two cars?
No. Each vehicle needs its own booking with its own registration.
UK airport barriers read number plates and match them to a reservation. A second car arriving on the same booking will not be recognised, and the barrier will not lift.
Some operators let you make two bookings in a single transaction, which is convenient for paying. They remain two separate reservations with two separate plates, and both must be correct.
Who should book?
Each driver, for their own car. That avoids the commonest group failure.
The failure is one person booking both vehicles under their own name, then entering the second registration wrong because they copied it from a text message at midnight. Each driver knows their own plate; let them type it.
Settle the money between yourselves afterwards rather than trying to reconcile it at the barrier.
What if the cars arrive separately?
At a self-park car park it makes no difference at all. Each booking is independent, each barrier read is independent, and the cars can arrive an hour apart without anyone noticing.
With meet and greet it matters, because a driver meets each vehicle. Two cars means two handovers and the operator needs to know. Tell them when you book rather than on the day, and ring about whichever car is running late rather than assuming they will connect two bookings.
What about different return dates?
Book each car for its own actual dates. This is where groups create expensive problems for themselves.
Copying the first booking because it is simpler, then having one party return two days later, means an overstay charge on a booking that could have been made correctly for a few pounds more.
If one person is flying home early or staying on, that vehicle needs different dates from the outset.
Which car park suits a group?
One car, a week or more — off-airport park and ride, where the daily rate does the work
Two cars, any length — official long stay, since you are paying twice and want the shorter transfer
Early departure with heavy luggage — meet and greet, booked for each vehicle
Mixed mobility within the group — the closest option you can justify, because the shuttle is the hard part
With two vehicles the transfer question doubles in weight. Everyone waits for everyone, and a bus that takes one car's passengers but not the other's is an irritating way to start.
Does it change with children across two cars?
Yes, and usually towards paying more. Car seats, pushchairs and tired children are harder to manage when the group is split, because people and luggage end up in different vehicles.
If that describes your trip, pay for the shorter transfer. The saving from a distant car park is small against coordinating two carloads of family onto the same shuttle before dawn.
A short checklist
One booking per vehicle, each with the correct registration
Let each driver enter their own plate
Check each car's actual departure and return dates separately
Tell meet and greet operators there are two vehicles
Agree who pays and settle afterwards
Confirm the terminal for everyone, at multi-terminal airports
Compare totals at Birmingham, Bristol or Luton with the number of vehicles in mind rather than the number of people. That is what you are actually paying for.