Jumbo crossword No 10

On my quest to do every single jumbo on the site, I've come to this a month late, but I'm here now! Very much found this a puzzle of two halves, in that the top went in quite easily while I needed to chip away at the bottom over several sessions - more about that later. Top five clues: 31a (made me laugh), 42a (cheeky!), 50a (nice and neat), 3d (cleverer than I initially thought!) & 18d ("where one fills in the gaps" is very good!). Some enjoyable stuff in here, but I've got some quibbles...