People trying to hail a black cab in London at night effectively face a curfew due to a lack of younger drivers, say London's business leaders.
Business leaders say the taxi's iconic status is under threat
Figures from the Chamber of Commerce and Industry (LCCI) show an ageing population of drivers refusing to work late nights and weekends.
The LCCI said it was causing a "severe shortage" of taxis in the city.
It has called for a modernised version of "The Knowledge" test and cash incentives to entice younger drivers.
LCCI chief executive, Colin Stanbridge, said: "While the London taxi remains at the heart of the capital's infrastructure, its iconic status is coming under threat.
"Our report reveals a worrying trend towards older drivers working fewer hours - particularly during the evenings - and reaching a peak at one of the capital's busiest times - Saturday night."
The report showed there were more licensed cab drivers aged over 70 than under 30.
But drivers under 30 work, on average, twice as many hours as those aged over 70.
Drivers under 50 are twice as likely to work until 2100 GMT, at least once a week, and 10 times more likely to work until midnight, compared with those over 50.
To reinforce its findings the LCCI also interviewed 200 licensed London cabbies face-to-face and 50 private hire operators over the phone.
This revealed that less than 20% of drivers worked later than 2100 GMT at least once a week and only 6% worked past midnight once a week or more.
To boost the number of young drivers the LCCI report recommended that the famously rigorous black cab driving test, The Knowledge, be made an accredited qualification.
It also called for more investment in the industry and an increase in the number of marshalled taxi ranks in central London at weekends.