Thank you to Scorpiojo and Sheep for your hints.
First I got 19d then 13d. I'm not sure about my answer to 20ac which may explain why I still can't get 16d.
Eventually the penny dropped with 15,25 and I felt ashamed of myself. I used to have a half share in one some 40+ years ago.
And I've just got 23ac as I type. Just two to go.