The Driving Standards agency (DSA) has researched the amount of hours learners need before they are ready for the test.
Recent research has shown that, on average, people who learn in a manual car ,take about 40 hours professional training, combined with plenty of additional practice, stand the best chance of passing their test.
For automatic driving this can be less, between a third and half the lessons of a manual car.
Note however that some people need more lessons and practice than others.
There are also those that have either a short or long term break between their lessons. This could be for any number of reasons. EG. Financial, Work Schedule, etc.
In extreme cases after a long term break of driving lessons, the above figures may have to be repeated over again.
Unfortunately, currently there is only a 43% overall pass rate and between 25% to 35% pass rate in the London test centres which means the first time pass rate is much lower.
The reason for such a low national rate is because candidates are not properly prepared.
You must be able to drive consistently well, with confidence and without any assistance or guidance from your instructor.
If you can't, then you aren't ready for the test.
Waiting until you are ready will save you time and money.
