Even having an oxbridge undergrad degree is not a ticket, though it may help to secure an interview, which is the first big hurdle. I doubt that every oxbridge graduate is rich and famous. Most prob end up doing similar things to all those who didnt go to oxbridge for undergrad.

Having said all that, im sure if you are good a bluffing how good you are you would prob be able to land a pretty good job in some far off land (prob in the far east as others have pointed out) with a PhD from Oxbridge (im sure it is worth more out of the UK/western world). If you get a good exchange rate, then you could prob live pretty comfortably of £25K for a little while (really depends on house prices). The main prob with that is any jobs that pay well will be in expensive cities so £25K wont go far.

Of course if you already are fantastic, then you prob dont need to worry about going far, as you will very soon be rich and famous.

PhD in Oxbridge? I only have an MSc in Oxford.