The short answer
For most content the double lesson is more efficient: of 45 minutes, the pick-up, adjusting the car and the drive out of city traffic all come off, leaving little practice time. Single lessons suit the beginning and tightly defined topics. Special drives are in practice always taken as a double.
"A driving lesson" means one teaching unit of 45 minutes — why it is counted that way is a separate post. The more practical question is how many of them to take at once.
What is left of 45 minutes
Meeting, adjusting seat and mirrors, briefly agreeing what is on: that is five minutes gone. Then the drive out of the dense area to wherever the topic can actually be practised, and the same drive back at the end. Starting in Bilk and wanting to practise roundabouts means spending a serious share of the unit getting there.
When a single lesson makes sense
- In the first few lessons, while concentration is scarcer than time
- For one clearly defined topic right on the doorstep — parking, hill starts
- When school or a shift leaves only a short window and the alternative is not driving at all
When the double wins outright
- Every special drive — motorway and cross-country are barely worth doing singly
- Whenever a topic needs repetition: the same junction three times in a row lands differently from once a week
- Before the test, because the test drive itself runs 55 minutes without a break
It usually only gets good in the second unit of a double. The first goes on arriving and revising, and then what was wobbling last week suddenly sits. People who only ever take single lessons almost always stop at exactly that point — and start the next one a step below it.
On stamina
Right at the start, 90 minutes is too long for many people, and that is not a bad sign. We begin with single lessons then and switch over once concentration holds. That change comes by itself for almost everybody, usually after a few appointments.
Billing is always by teaching unit — a double lesson is two of them, not a package. The rates are on the price page.
What to take away
Double lessons are not more expensive, they are two units instead of one — and they usually deliver considerably more than twice the actual practice. The exception is the beginning: while concentration is scarcer than time, the short lesson is the better one.