The Crossword Editor has replied:
I fear that you are quite right. I am getting it corrected ASAP. Meanwhile here is a version of how the puzzle was intended to look.
The attached Word document contained these clues at the end:
20.Hirst's original work? (7)
21. Hull bird admitted to Royal Society (7)
22. Last stand (6)
25. 29 egg supplier, say, banned after Revolution (5)