Behavioural weight management programmes can help people lose weight and reduce their risk of chronic diseases, but programmes led by specialists in clinical settings can be too costly for the NHS to deliver at the necessary scale. There is good evidence that primary care referral to commercially available open-group behavioural weight management programmes (like Weight Watchers or Slimming World) is a cost-effective option and 12-week referrals to these programmes are often used in the NHS. However, there is debate about whether a 12 week programme is sufficient to have a long term impact. In the WRAP trial we evaluated whether an extended referral (52 weeks) is more effective and cost-effective over 2 years.