The number of screening centres for the sexually transmitted infection chlamydia is to double, the government has announced.

The new centres are a further step towards a national programme.

Junior Health Minister Lord Hunt announced the sites would be opened by the end of the year in addition to a first wave of 10 centres.

They were opened after results from two sites in Portsmouth and the Wirral found almost one in 11 women were suffering from the disease.

Up to 10% of young women between the ages of 16 and 24 don't know that they have the infection Lord Turnberg

There are often no obvious symptoms of chlamydia.

But there can be serious long term complications for women. It is the most common cause of infertility and ectopic pregnancy.

Treatment rates

The first 10 sites targeted women aged 16 to 24 as young women, particularly those under 21 are at the greatest risk of infection.

Initial results from Portsmouth and the Wirral found 75% of those offered screening accepted.

Around 95% of those diagnosed with chlamydia returned for treatment.

Announcing the second wave of centres, Lord Hunt told the House of Lords: "We will review the progress of the screening programme in the light of the introduction of the 20 sites we are now committed to.

He said the two pilot programmes had been "very successful".

Lord Hunt added: "The prevalence of women in the target age range at general practice was 8.5% and 8.7%.

"That is a very significant figure."

He said most had been successfully treated with antibiotics.

National programme

Lord Clement-Jones, Liberal Democrat health spokesman, said there had been a 122% rise in chlamydia in the past 10 years.

He said it was crucial the government introduced a national screening programme from the target date of 2004/5.

Lord Turnberg, a former chairman of the Public Health Laboratory Service, said the screening test was simple and treatment easy, adding it was important to spread awareness of the condition.

"Up to 10% of young women between the ages of 16 and 24 don't know that they have the infection."