Do the members of the Cornley Drama Society ever write their own plays? Some of their plays are explicitly by other people, but I definitely get the sense that the members of the drama society occasionally dabble in scriptwriting themselves.
My personal opinion:
Definitely not by the society: The Murder at Haversham Manor (the society chose it for having the required number of roles), Peter Pan (the programme attributes the adaptation to Susie HK Brideswell, who also wrote Haversham Manor), The Pilot (a pre-existing play that has previously been criticised for its inaccuracies), The Most Lamentable... (by a Shakespeare), Chris's insect ballet (the man is not a choreographer), Annie's farce (from the 1970s).
Probably not by the society: Harper's Locket (it just doesn't feel to me like something the drama society would write), The Lodge (if they'd written it themselves, they could have extended it to fit the runtime in ways other than adding adjectives), 90 Degrees, There Is No Escape (I find it hard to envision them writing plays set in America!).
Grey area: A Christmas Carol - it's possible that they technically created the adaptation themselves, but I think a lot of the dialogue comes straight from the original text.
Could go either way: A Trial to Watch.
Probably by the society: The Spirit of Christmas (one of Robert's 'this is not your best work, Chris'es is timed in a way that makes me feel Chris wrote the play himself), The Nativity (obviously the story is pre-existing, but the exact script is probably by the society, particularly considering the Brookshaw Corporate Finance plugs), Summer Once Again (Robert definitely either wrote this himself or heavily rewrote it to make his own role more prestigious and Chris's role more humiliating), Jonathan's circus number (calls on various skills that members of the society presumably have; either he tailored it to them himself or he really didn't think this through!).
Definitely by the society: Max's kitchen sink drama, Dennis's toothpaste play, Sandra's audio drama.