I took no lessons. My son took maybe 10 and passed first time. (He did a lot of practice in our car). My ex, not sure but way more than 12.
All the Americans I work with did like me, read the book, asked a few questions then jumped right into the exam with out lessons and passed.
So a lot depends on the individual, how much 'wheel' time they get with SO's, mom/dad's cars, etc.
My personal feeling is the driving instructors (not all but some) will milk it. Witness my ex, she had lesson for years. I finally convinced her to change instructors and several lessons later, she was able to sit the test and passed. I think some are just there like babysitters for the car, others are a credit to their profession and actively teach.
My advice is
1. If you don't think your driving is improving with an instructor after x number of lessons, find a new one.
2. Get as much 'wheel' time as possible. Drive, drive, drive and then drive some more. Any time you go out in the family car - drive. An hour or two with an instructor only will take a long time to get experience.
3. There are 1 week intensive courses. I can't comment on price but they are about 30 hours+ of being the wheel.
As a comparison, the AA recommends 44 hours with a driving instructor PLUS another 22 hours private practice. I think this is way over the top as I can get my Private Pilot License with 32 hours of lessons, including 10 hours of solo flight!