There has been much concern recently in the UK about the decline in the number of students studying physics beyond age 16. To investigate why this might be we used data from a national database of student qualifications and a multilevel modelling technique to investigate which factors had the greatest impact on the uptake of physics at Advanced Level (A-level) in a particular year. Each factor of interest was entered into a separate model, while accounting for prior attainment and gender (both well-known predictors of A-level uptake). We found that factors associated with greater probability of uptake included better attainment in physics (or combined science) and maths qualifications at age 16 in comparison to other subjects, and (for girls only) attending an independent or grammar school. While it is difficult to address these factors directly, the results imply that more needs to be done to improve relative performance at General Certificate of Secondary Education, perhaps by increasing the supply of specialist physics teachers at this level and to overcome the perception (especially among girls) that physics is a particularly difficult subject. (Contains 4 notes, 5 figures, and 7 tables.)