Snowy Owl,
I guess the final number will depend on the number of people that Bond would like to interview, but it may also vary slightly by the quality of candidates. I don't think Oxford will want to send forward any candidates who they doubt have the ability or motivation to succeed. On the other hand if the standard is very high they may want to send a larger selection for Bond to make the final selection on. Just my guess really.
If you think that 48 went for stage 2 and there are 12 places then 1 in 4 are actually really good odds. Out of the 48 you might be surprised at how few have done really well at everything, so being a bit weak in one area might not finish someone's chances. Good Luck.