Cryptic crossword No 1,393

Hey Tug, I thought I'd pop in to give your puzzle a go. While there were clues to admire, eg 12a, 16a, 23a, 25a, 27a, 7d, 19d, overall I found it a bit of a curate's egg with issues to do with technicalities, surfaces and some details. Let me explain. SPOILERS...

Thanks Tug, some tough stuff in there - favourites for me 12a, 18a, 23a, 25a, 26a, 27a (COTD), 5d (nice Lego), 7d, 19d & 21d. Spoilers ...