Here's hoping will37 has had enough time to finish this, which is more than I have. So I seek a hint or two. I have the "instruction" in the usual place (and marvel at its achievement). However filling the other two clash cells is taking more hours than it should. I infer that more than just two letters occupy each of these cells (because the across instructions seems to mean that). Does each of the two cells lead to an anagram, or are both to be lumped together? The problem really arises because I can't for the life of me get anywhere with 15, 7 or 27. Which is no doubt where the PDM is lurking. Oh dear!