Cryptic crossword No 2,042

Special instruction is an addition to the puzzle, and not needed to solve it at all. Hints to follow:

Thanks for the fun puzzle Fudgeller, which I really enjoyed. If you like you can see/hear me solve it at twitch.tv/contocrosswords - if you do I hope it's fun/useful!

Crikey. I completed the puzzle and then read your Comments. I have to commend you on the grid fill though the SI beat me completely. Some tricky words to clue and, on the whole, a solid job done. 15a, 23a,3d my podium. Thanks. PM

Hell of a gridfill, nicely done; I twigged what was going on early enough for it to help me with 15a & 18d, and the fact that they're not even *too* obscure means you've done a cracking job. Big ticks for 17a, 26a, 1d, 3d, 4d & 21d, but it was all good stuff throughout. Thanks for the fun!