In order (source: Wikipedia):-
Winston Churchill - Royal Military Academy Sandhurst
Anthony Eden - Bailliol, Oxford
Harold Macmillan - Bailiol, Oxford
Sir Alec Douglas-Home - Christ Church, Oxford
Harold Wilson - Jesus, Oxford
Edward Heath Bailliol, Oxford
James Callaghan - Took the Oxford entrance exam, but didn't have the money to attend.
Margaret Thatcher - Somervillle, Oxford
John Major - didn't go to university
Tony Blair - St John's, Oxford
Gordon Brown - Edinburgh
David Cameron - Brasenose, Oxford.
Of that twelve, eight went to Oxford. It was nearly nine but for Callaghan taking civil service exams instead. None went to Cambridge, although it depends on if you include Nick Clegg who was at Robinson, Cambridge. He's not prime minister but that might depend on whether Cameron has a bizarre accident with a windmill and a bicycle.
Oxford has also supplied us with the current back-ups. Boris Johnson (Balliol ) and both of the Milibands (Corpus Christi) and Ed Balls (Keeble) and Osborne (Magdalen). It's a very long shot indeed, but if you fancy Louise Mensch's chances, she went to Christ Church, which would nudge that college up in to second place behind Balliol, while Michael Gove would be a first showing for Lady Margaret Hall. Probably not in the running, but Theresa May went to St Hugh's and Hague, like Osborne, went to Magdalen.
If BoJo ever gets through the magical door, it will take Balliol's score to 4 which will be very difficult for any other college to match unless Balliol is disqualified for the next sixty years. Yvette Cooper (Mrs Ed Balls) is also Balliol, so the college is uncannily good at spotting potential contenders.
Looking at the two who didn't go to university - Callaghan and Major - the lack of an Oxford degree doesn't seem to have made a difference to their performance as PM. Both took other professional exams, both were wrong about a significant number of issues and lost office as a result.
Winston Churchill doesn't really count in this sequence. Since he passed out of Sandhurst 20th in his year of 130, he was no slouch. Luckily for us, since he didn't go to Oxford his idea was to fight Germany rather than defend ourselves by being pre-emptively invaded by Soviet Russia. Sadly, he eventually lost that half of the war but not for want of trying. Baroness Thatcher went to Oxford but gets a special pass because she studied a proper subject: Chemistry.
Outside of No 10, a mention must be made of Baroness Shirley Williams (Somerville) and Baroness Mary Warnock (Lady Margaret Hall), architects of the worst aspects of the education system which, sadly, was signed in to existence by Mrs Thatcher who was rather trusting in those days and thought the teachers and civil servants knew what they were doing. Perhaps they did.
So let's hear less about "Oxbridge" as if they were both equally culpable. It's incontrovertibly Oxford which has landed us with the majority of front-rank noodles.
Or maybe not.
Part II - A bouquet of Chancellors
Update: Helen Mirren has read for the part of the Queen, again, in a drama which follows the relationships of the monarch to her prime ministers.