It is a bit of a misnomer to speak of “Oxbridge admissions” since undergraduate admissions are controlled by the colleges. The university establishes ‘matriculation’ requirements but these are floors. Hence, while some colleges may like ‘legacies’, other colleges (Magdalen at Oxford, Kings at Cambridge) actually appear to give children of older members a harder time.
In a similar vein, while many UK universities claim they only consider ‘objective’ information like examination results, this isn’t true. ‘Contextual’ information is important as is evidence of independent thinking and scholarship etc.