This study applied a theory-based questionnaire to examine the behaviours and beliefs of all practice staff who may be involved in offering chlamydia screens to young people aged 15-25 years old. We aimed to identify potential influencing factors and examine the organisational constraints, which may be amenable to change. The National Chlamydia Screening Programme offers opportunistic screening to men and women between 15 and 25 years old who have ever had sexual intercourse and primary care is the second largest source of screens. In England 15.9% of the target group were screened against a target of 17% in 2008. Interventions to improve the frequency of offers have shown effects with volunteer practices. A survey of 85 General Practices was completed by 55 doctors, nurses and receptionists. Interviews were conducted with 12 staff from three practices. Respondents were unable to identify the national screening target. Only half record if a patient is sexually active. Half the sample had some recollection of the frequency of offers they made, with a mean of 4 per month. These were predominantly in consultations concerning sexual health. Perceived social norms are favourable to screening and respondents have strong perceived control over offering screens, including to those under 16 who are sexually active. Attitudes towards screening were positive but disadvantages and barriers related to increased pressure on practice resources for longer consultations and contact tracing. There were no differences in beliefs and practice behaviours between medical and nursing staff. Future interventions should be targeted at increasing the range of consultations in which offers are made, demonstrating how to make offers without increasing consultation time, providing more complete records of sexual activity, screens and results, and encouraging audit and review within the practice to promote practice wide approaches to increasing opportunistic screening.