As many as 29% of drivers aged 18-30 said they were unprepared to drive alone after their test, the Co-operative Insurance survey found.
Also, 24% said an accident they had could have been prevented if they had spent more time learning to drive, with 62% in favour of a minimum learning period.
Based on responses from 2000 drivers aged 18-30, the poll also showed that 21% avoided motorways after passing their test, while 14% considered themselves to be "unprepared" to drive at all.
Also, 29% felt unready for night driving, 21% felt driving lessons did not prepare them to drive with passengers, 19% avoided city centres, 14% could not face driving in the rain and 8% avoided right turns.
A total of 18% passed their test after spending three months or less learning.
James Hillon, director of general insurance at Co-operative Insurance, said: "A lot of public debate is taking place on how safety can be improved and insurance premiums cut for young drivers, but the views of young motorists themselves are rarely heard.
"Far from being the stereotypical image of the 'boy-racer', this study shows that many are not confident to face everyday situations on Britain's roads in the early years, despite months of lessons."
He went on: "Young people say that the current system fails to prepare them for driving on motorways, on their own or in poor conditions. They want to see a more comprehensive approach and are hugely in favour of a minimum learning period for all new drivers to fully prepare them and we fully support this."