David: as other people have suggested 26A requires the use of an apostrophe; 5A the clue means 'move quickly' and the answer achieved by inserting a letter into a word to do with preventing stationary boats from moving about; I struggled with 8D too, mostly because I'd carelessly worked out my anagram for 11A and written in a more familiar form of the word. The clue means 'relatives'.
Overall, I found this puzzle 'steady', in other words, difficult but not so difficult that I didn't make progress. It took me an inordinate amount of time to get 15D, especially annoying as I've read the work in question. Perhaps, if I hadn't misspelled 18A (my COD) I wouldn't have taken so long.
But I have totally failed on 23A, despite resorting to electronic word searches. I can only think that I've got one of my crossers wrong but I'm sure of my first letter 'B' - confident of my middle 'A' and my final 'P' fits and parses in 20D.
No-one else seems to have mentioned this clue, so I assume that I'm missing something obvious, or have made, yet another, careless mistake.
BTW anyone care to parse 4D? The way it parallels 9D strongly suggests we have our regular setter, or perhaps, someone following a newly established 'house style'?