It's probably the most noticeable building on Harrow's High Street. Not the largest, but the eye is drawn to it being set back behind the well-manicured garden, so it invites you to guess its purpose. Someone unfamiliar with the area might easily assume it was where the school was centred, and anyone who has ever travelled along Harrow's High Street would probably recognise it. Likewise anyone has ever gone through Eton, which is very small, having only one through road, would realise that as the pictured building is evidently not a Tudor building, accommodation block or a modern addition, it must be somewhere else. You perhaps don't get out much from your central London bubble, but probably best not to assume that no one else passes by notable buildings on main thoroughfares elsewhere and might consequently recognise them.