Hepatitis C among young drug users in London is reaching epidemic levels while HIV cases are "worryingly high", researchers have warned.
One in four said they had shared a needle in the last month
A study in the British Medical Journal found two in five new drug users have hepatitis C, which damages the liver.
It also showed 3% of injecting drug users have HIV.
Researchers blamed the government's drug policy. But a government spokesman said it was committed to driving down cases of hepatitis C.
'New programmes needed'
Researcher Dr Ali Judd, of Charing Cross Hospital, west London, said: "Hepatitis C is now spreading at epidemic levels across London and HIV incidence is worryingly high, which if unchecked will lead to an increase in the total number of HIV infections.
"There is an urgent need for new and comprehensive programmes to tackle this growing number," she added.
The research was conducted by a team from Imperial College London, the Health Protection Agency and the London School of Hygiene and Tropical Medicine.
Tests were carried out on 428 drug users who had been injecting for up to six years.
It was found one in four reported sharing a needle in the past four weeks. Both hepatitis C and HIV can be spread in this way.
Dr Matthew Hickman, from Imperial College London, said government drug policy has focused on drugs and crime for the past six years.
"There is a need now to reinvigorate harm reduction policies that prevent transmission of hepatitis C and HIV," he said.
A Department of Health spokeswoman said almost £500m will be spent on drug treatment from 2004 to 2005 .
She said: "The extra funding in the last few years has led to many more drug users engaging in treatment and an increase in the numbers successfully completing treatment."