Hiya,
Just eating a double decker and was thinking about the whole raisin thing so googled and found this thread.
I emailed cadburys back in Jan 2003 about this and they changed the recipe in 1986 after consumer research - though I don't recall being asked They first came out in 1978 if anyone is interested/cares
Reckon they should do a limited edition with the raisins back in...