Aims/hypothesis To describe the clinical characteristics of adults with type 1 diabetes admitted to hospital and the risk factors associated with severe COVID-19 in the United Kingdom. Methods A retrospective cohort study was performed using data collected through a nationwide audit of people admitted to hospital with diabetes and COVID-19 conducted by the Association of British Clinical Diabetologists (ABCD) from March to October 2020. Pre-specified demographic, clinical, medication and laboratory data were collected from the electronic and paper medical record systems of the participating hospitals by local clinicians. The primary outcome of the study, severe COVID-19, was defined as death in hospital and/or admission to the adult intensive care unit (AICU). Logistic regression models were used to generate age-adjusted odds-ratios. Results Forty UK centres submitted data. The final dataset included 196 adults who were admitted to hospital and had both type 1 diabetes and COVID-19 on admission (male 55%, white 70%, mean (SD) age 62(19) years, body mass index (BMI) 28.3(7.3) kg/m2 and last recorded HbA1c 76(31) mmol/mol or 9.1(5.0)%. The prevalence of pre-existing microvascular disease and macrovascular disease was 56% and 39% respectively. The prevalence of diabetic ketoacidosis on admission was 29%. A total of 68 patients (35%) died or were admitted to AICU. The proportions of people that died were 7%, 36% and 38% of <55, 55-74 and >=75 year olds respectively. BMI, serum creatinine levels and having one or more microvascular complications were positively associated with the primary outcome after adjusting for age. Conclusions/interpretation In people with type 1 diabetes and COVID-19 who were admitted to hospital in the UK, higher BMI, poorer renal function and presence of microvascular complications were associated with greater risk of death and/or admission to AICU. Risk of severe COVID-19 is reassuringly very low in people with type 1 diabetes under 55 years of age without microvascular or macrovascular disease.