A whistleblower has lifted the lid on the practice which allows under-qualified instructors to teach learner drivers on the road.
Experienced instructor Adrian Lewis says it is "disgraceful" trainee instructors can legally give paid-for lessons to pupils for up to six months.
The Catford-based instructor claims it is no surprise Lewisham has a low test pass rate when many rookie instructors are "more nervous" than the learner driver.
Anyone training to be a driving instructor must pass three exams an advanced driving test, a theory test and a written teaching exam.
After passing the first two of these tests, the student can apply for a trainee licence.
This allows them to teach pupils on the road for six months even if they have not passed the teaching exam.
Mr Lewis, of Fordel Road, Catford, believes this is a dangerous practice.
He said: "I think it is disgraceful. It leads to a situation where the instructor is more nervous than the learner.
"The teaching exam teaches you how to control a pupil. If you don't pass this how can you be in full control of a lesson?"
Earlier this month News Shopper revealed just 35 per cent of tests taken last year at the borough's Hither Green test centre were successful.
Mr Lewis, who has been an instructor for five years, said: "People stand a better chance of passing if they are being taught by a fully-qualified instructor rather than a trainee.
"The public are being ripped off."
He added: "This is not going to make me popular with instructors but I don't give a monkeys.
"It is something the fee-paying public has a right to know."
Mr Lewis also says many pupils book blocks of lessons but are forced to change their instructor halfway through because their original instructor's six-month trainee certificate expires.
The Driving Standards Agency says all potential instructors must display a pink certificate in their windscreen, saying they are a trainee.
Bur Mr Lewis claims this code is not recognised by most learners and thinks instructors should tell their pupils they are not fully qualified.
BSM, the country's largest driving instruction firm, says it provides more than 50 hours of tuition to its trainee instructors.
A spokesman added six months should give "sufficient time to take and pass the qualifying exam".
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