Last one: 5ac Some person ought to stop casual additions to fat cats'bonuses. (7) I have
* O* G* T*
Happier to have hint rather than answer ( as with Guardian Prize crossword)
Thanks, stevea600 and Malone! The extra 'to' was a late-night typo on my part but I had still wrestled with it. As usual with cryptic clues, the impossible becomes blindingly obvious once solved!