We examined the link between several adiposity measures − BMI, fat mass, body fat percentage, fat mass index, waist and waist to hip ratio) taken at baseline visits over a decade ago to risk for COVID-19 positive tests that occurred in hospital in the UK biobank. Overall, 793 participants tested positive in a hospital setting out of 380,976 participants. Poisson models with penalised thin plate splines were run relating exposures of interest to positive tests in hospital, adjusting for confounding factors. Each measure of adiposity was associated strongly with positive in-hospital test, in a broadly linear fashion, despite the model allowing for non-linear associations. There was a stronger gradient of risk across BMI (Pinteraction=0.09) and fat-mass index (Pinteraction=0.048) in men compared with women. Compared to a referent of 21 kg/m2, men with BMI of 30 kg/m2 (RR 2.08 95% CI 1.84-2.36) and 35 kg/m2 (RR 2.80, 95% CI 2.36-3.31) were at higher risk; corresponding RRs for women were 1.36 (95% CI 1.49-1.63) and 1.86 (95% CI 1.59-2.17). The associations between BMI and COVID-19 were largely consistent by age group and ethnicity. These data add further support for linear links between excess body fat and more severe COVID-19 outcomes across differing groups.