I nearly gave up on this once or twice due to the excess of cold solving required to get a foothold on the grid filling. A thematic in the lower part of the grid led me to the PDM. Several clues had me stumped for hours, and without the PDM I would still be struggling to get those. A brilliant and, for me at least, a VERY difficult puzzle. As stated previously, the preamble, although fair when the puzzle is completed, is distinctly unhelpful in starting it. I too, initially, had dozens of clashes. After last weeks I was so glad that I did not require the further frustration of hours of grid staring.