"till Tom stops ringing"
'Tom Tower', Christ Church College, Oxford
Creative Commons Attribution Share Alike'Tom Tower', Christ Church College, Oxford - Credit: Philip Talmage, Wikimedia Commons

'The House' is the Oxford college, Christ Church.

'Great Tom' is a bell in Tom Tower, which forms part of the main entrance to Christ Church. Traditionally, 'Great Tom' was sounded 101 times at 9.05 p.m to summon students back to their colleges for curfew.

Discipline at Oxford colleges in this period was taken seriously and transgressions were dealt with by special officers of the University, known as proctors, and by the Bulldogs (the University's private police force).