As I've become older, I've learned that willingness to seek argument itself demonstrates a lack of maturity, regardless of how correct you might be. In recent years, this has led me to read this website less and less, which used to be an excellent source of information for keen wannabes in the late 90s and early 2000s.
There is a simple recruitment criteria above all others - it's no secret and it cannot be faked. Would I sit next to this chap / lady for 12 hours, then go for a beer with them downroute.
All the answers you need are on the BA site, and the three FTO sites, refined by 2 years of questions directly to the recruitment team. You don't need to read / post to this website to get in and it certainly won't give you the final "edge".
Any competitive process can be as picky as it likes to reduce applicants to manageable numbers, but don't feel bitter about it - choose another route and aspire. Having said that, there is no requirement to have read aero engineering at uni, glided with the Air Cadets, or achieved the dazzling heights of AAAAs at A-Levels. Some lucky souls have those achievements in spades, but most UK pilots are normal with a passion for aviation. Don't be put off from applying if you have the minimum - that is the cutoff and nothing higher.
Finally, most "authoritative" sources in this thread are full of speculative guesswork. Get yourselves to a school visit and ask people in the know instead of on an anonymous forum.
Bon chance!