Strain B.1.1.7 of SARS-CoV-2, a variant first detected in the UK in September 20201, has spread to several countries across the world. Several studies have established that B.1.1.7 is more transmissible than the pre-existing variants, but have not identified whether this leads to any change in the severity of the disease.two. Here, we analyzed a dataset linking 2,245,263 positive SARS-CoV-2 community tests and 17,452 COVID-19 deaths in England from September 1, 2020 to February 14, 2021. To 1,146,534 (51%) of these tests, the presence or absence of B.1.1 .7 can be identified because of mutations in this lineage, preventing PCR amplification of the spike gene target (failure of the S gene target, SGTF1) Based on 4,945 deaths with known SGTF status, we estimate that the risk of death associated with SGTF is 55% (95% CI 39-72%) higher after adjusting for age, sex, ethnicity, deprivation, home residence, authority place of residence and date of the test. This corresponds to the absolute risk of death for a 55-69 year old man, increasing from 0.6% to 0.9% (95% CI 0.8-1.0%) in 28 days after a positive test in the community. Correcting the incorrect SGTF classification and lack of SGTF status, we estimate a 61% (42–82%) higher risk of death associated with B.1.1.7. Our analysis suggests that B.1.1.7 is not only more transmissible than the pre-existing variants of SARS-CoV-2, but can also cause more serious illnesses.