Both CSSA and the Independent Trials now have a security period for handing back the papers - permanently. Used to only be the Independents but now is both.
At my school the procedure will be that we hand back the paper, get the students to check the answers and adding up, and then we will collect them again and keep them until the end of the security period when we will give them back permanently.
Of course, as a teacher, I will have made notes on strengths and weaknesses of individual students and the cohort collectively to see what I need to concentrate on teaching over the rest of the term.
Not all schools do the Trials at the same time and some schools haven't even started theirs yet but they may be using the Independent or CSSA papers - particularly the Independents.