Background England has experienced one of the highest rates of confirmed COVID-19 mortality in the world. SARS-CoV-2 virus has circulated in hospitals, care homes and the community since January 2020. Our current epidemiological knowledge is largely informed by clinical cases with far less understanding of community transmission TRANS. Methods The REal-time Assessment of Community Transmission TRANS (REACT) study is a nationally representative prevalence SERO survey of SARS-CoV-2 virus swab-positivity in the community in England. We recruited participants regardless of symptom status. Results We found 159 positives from 120,610 swabs giving an average prevalence SERO of 0.13% (95% CI: 0.11%,0.15%) from 1st May to 1st June 2020. We showed decreasing prevalence SERO with a halving time of 8.6 (6.2, 13.6) days, implying an overall reproduction number TRANS R of 0.57 (0.45, 0.72). Adults TRANS aged TRANS 18 to 24 yrs had the highest swab-positivity rates, while those >64 yrs had the lowest. Of the 126 participants who tested positive with known symptom status in the week prior to their swab, 39 reported symptoms while 87 did not, giving an estimate that 69% (61%,76%) of people were symptom-free for the 7 days prior testing positive in our community sample. Symptoms strongly associated with swab-positivity were: nausea MESHD nausea and/or vomiting HP and/or vomiting MESHD, diarrhoea, blocked nose, loss of smell, loss of taste, headache MESHD headache HP, chills MESHD chills HP and severe fatigue MESHD fatigue HP. Recent contact with a known COVID-19 case was associated with odds of 24 (16, 38) for swab-positivity. Compared with non-key workers, odds of swab-positivity were 7.7 (2.4, 25) among care home (long-term care facilities) workers and 5.2 (2.9, 9.3) among health care workers. However, some of the excess risk associated with key worker status was explained by recent contact with COVID-19 cases. We found no strong evidence for geographical variability in positive swab results. Conclusion Our results provide a reliable baseline against which the impact of subsequent relaxation of lockdown can be assessed to inform future public health efforts to control transmission TRANS.