I've had time to scan the index of Thompson's *The First Philosophers*, and while there are several references to "science and ideology," none show up the reference I vaguely remember. I'll check his books written after the impact of Mao on his thought (he and Joan Robinson co-edited a journal on China, which I have never seen)--when I can locate them, my book shelves are a shambes.. I'll also check his first Marxist work *Aechylus and Athens*.
If it doesn't show up there, I'll start checking through Caudwell's *Studies in a Dying Culture* to see if it wasn't Caldwell himself (I don't believe it would be in any other Caudwell work). I'll be back to you when I find something (or when I definitely don't).
Carrol