By Nick Triggle
Health reporter, BBC News
People with chlamydia might not have any symptoms
Millions of pounds have been squandered on the national chlamydia screening programme, a watchdog says.
The National Audit Office said the NHS had duplicated effort and failed to test as many of the under-25 target group in England as it should have.
Last year £17m could have been saved, nearly half the sum spent, if the programme had been better run, it said.
But the government said such an "ambitious" screening programme was always going to take time to perfect.
The programme was set up in response to rising rates of the so-called silent infection - it often shows no symptoms but if left untreated can cause infertility.
The screening was initially introduced in several pilot areas in 2003, before being rolled out nationally in 2007. So far £100m has been spent on it.
But the NAO said despite the four-year trial period, the health service failed to learn lessons.
The 152 NHS trusts responsible for delivering the programme should have worked in partnership more, the watchdog said.
Money could have been saved by setting up a more centralised purchasing arrangements, while resources had been wasted on developing different branding and advertising campaigns, it said.
Questions were also raised about how the actual screening was done.
The programme was designed to reach out to people not using sexual health clinics and so health officials went out to places like bars and clubs to encourage young people to come forward.
But the NAO said there was little evidence that this had proved effective.
NHS chiefs also struggled to get GPs fully engaged - they are not paid to do the screening under the terms of their contract although some trusts resorted to paying them extra to get involved.
The problems meant the programme had failed to reach as many people as it should have - something already well documented.
In the first year of the national programme - 2007/8 - just 5% of the 15 to 24-year-old population was screened, well short of the 15% target.
The following year it was made a priority by the government and screening rose to 16%, although that was still short of the 17% target.
The poor reach of the programme and duplication of resources meant the average cost of each test last year was £56, rather than the £33 experts say it should cost.
The highest figure recorded by a trust was £255 per test.
What is more, the NAO noted that it appeared one in 10 of those who tested positive did not receive follow-up treatment, rendering the screening pointless.
However, the watchdog admitted this could just have been because the NHS had not recorded their treatment.
Mark Davies, from the NAO, said the piloting of the programme had been a "waste of time" as the problems identified by the watchdog should have been addressed before it was expanded.
Edward Leigh, chairman of the House of Common's Public Accounts Committee, which will now be looking into the issue, added: "This is a classic example of what can go wrong when a national programme is rolled out unthinkingly."
But Public Health Minister Gillian Merron said it was good that the reach of the screening had improved.
She added: "An ambitious new programme on this scale takes time to perfect and must continue to improve."
Neither Scotland, Wales or Northern Ireland has set up a national screening programme on such a scale.