On my day there was around 15-20 people in the group. We can make educated guesses all we like but we're never going to know the true number. Considering there's only 10 spots available it seems to me that a "generous" amount of people have made it to the assessment centre stage (like 30%?, although that's just me pulling a number out of thin air). Earlier I noticed someone mentioned that they'd heard only 70 made it to the assessment centre stage, no way it's that low. Not too surprising really when you consider the only criteria they've had for filtering applicants up to now has been based off online competency tests (doesn't really tell you anything about the applicant other than they have the very basic skills needed).