I was at OAA last December and there were just short of 30 of us on the day. However, there were a lot of assessment days. A couple of us worked out that there was probably in around 1000 assessed at Oxford alone. It was difficult to tell as when we were booking our assessment day, we were unable to see the days that were already full. However, the assessments ran through the end (I think?) of November to the beginning of January. So, if 25 people were assessed per day, Monday - Friday, for roughly 6 weeks, it's my best guess that there were around 1000 in total.
I'm not sure how accurate the FTE figure of 240 is but it seems ok Probably a bit small if anything. Bear in mind however that FTE was/is the smallest recruiter by a long shot - CTC the largest. Again, an educated guess - I'd say there were around 1500 at CTC.
Since there was around 3000 assessed between the three schools a lot of people began to raise eyebrows at just how legitimate their chances were. If you read back to around December on this thread you'll see various rants about the cost of the assessment and it's value. It's true, FTE, CTC and OAA must have made a substantial amount of money but it'd be unfair not to assess somebody with the minimum qualifications and a decent application.
Don't let the numbers deter you! They shrink very fast.