Twice in the past I was part of teams entered for University Challenge; however we never got past the earliest stages. So I take the news that one of this year's winning team may not have been eligible (BBC News: BBC in University Challenge probe) with interest.
My memory from both entries is that the forms were filled in around about March/April time, then we went to the off-screen auditions in about May. The possibility that by the time the final was reached some of us may no longer have been students (whether due to graduation or failing the year) was there, especially as our enrolment was always for one year at a time (which in other spheres has resulted in the annoyance of having to renew some archive access cards every year). However we were always told that one had to be a student at the point of entry. As far as I am aware the rules have not changed since. There is probably nothing in this story beyond ill-informed journalists digging for scandals.
The real point of outrage about this year's University Challenge winning team is not the fact that one of the members has graduated since entering or Gail Trimble's knowledge but that Oxford and Cambridge are allowed to send multiple teams from the individual colleges, whereas other universities can only enter on a university wide basis. Ironically it was this year's runners' up, the University of Manchester, who famously protested this rule in 1975 when their team answered every question with either "Trotsky", "Lenin", "Karl Marx" or "Che Guevara". Here's to putting the universities on an equal footing.