Agree with all the observations so far today, but would add that 5d is one of the worst, semi literate, attempts at a cryptic definition I've ever seen. Liked 13d though
I agree about the extra letter in 26, and I don't like the clue much anyway.
The wren in 12d is a bird, though I'm not sure if the clue is biologically accurate. If you haven't heard of this assembly, it would be difficult to solve.