A levels: Standard offers range from AAA to A*A*A, with required subjects set by each course. Physics asks for A*A*A, with A* in Mathematics and Physics.
The IB: Usually 38 to 42 points, with 6 or 7 in relevant Higher Level subjects. Physics asks for at least 40, typically 42, with 7 in Mathematics and Physics and 6 in a third subject, all at Higher Level.
U.S. qualifications: Imperial looks for AP exams, usually with scores of 5, alongside your high school diploma, in subjects your course names. Physics asks for five 5s, including Calculus BC and both Physics C exams, or three 5s plus an SAT or ACT score. Imperial’s pages differ on whether SAT or ACT scores count, so ask its admissions team before you rely on one.
English: Each course sets a Standard or Higher English requirement, which you must meet even if English is your first language. Physics asks for the Higher level.