Background and Aims: An estimated 270 000 people in the UK live with hepatitis B infection, the leading global cause of liver cancer. In 2022, opt-out hepatitis B testing was introduced in emergency departments (ED) in London. We conducted a 2-year multicentre evaluation of this programme across seven sites. Methods: Adults testing positive for hepatitis B surface antigen (HBsAg) through ED opt-out testing (n = 983) were compared with those referred via non-ED pathways (n = 416) over at least 12 months in the same regions with a six-month follow-up period. Demographics, clinical characteristics and factors influencing time to assessment were analysed. Results: ED testing led to a 107% increase in HBV assessments. Of 983 HBsAg-positive individuals, 90.2% (887/983) were contactable and 97% (660/679) of those requiring assessment were linked to care. 35% were aware of their diagnosis but not under specialist care. Among ED-diagnosed individuals, 16.37% had significant fibrosis and 20.45% had viral loads > 2000 IU/mL. ED referrals were older (mean age 51 vs. 47 years, p < 0.001) and had lower viral loads (mean log10 HBV DNA 2.08 vs. 2.78, p < 0.001). Mean time to assessment in the ED group was 90 days. Conclusions: ED opt-out testing has doubled new assessments of hepatitis B cases, identifying individuals who would benefit from surveillance and/or treatment. Linkage-to-care rates were very high, though time to assessment was prolonged by service factors. A significant proportion were aware of their diagnosis but lost to care, underscoring the need for services which can maintain engagement.