Please treat this as a response to post 34 from numbskull. I have submitted as a very despondent seal.
I had assumed that the grouping was by quadrant positioning rather than number order. So I had struggled but got somewhere on the NE corner. I had put the answer to 4 across in the right place; inserted the answer to 6 down at 5d; and 5 down at 6 down. I was able to slot in an answer at 11 a , 13a, 7d and 8 down and had the first threes letters of 9 d.
Now I am hopelessly stuck. Is the above wrong? I think I may have to give up. It will be lovely weather on the Norfolk sandbank mid-week.
Can someone help me with 16 down and 22 ac and do these all slot into the central cross?
A bad week alas. I do wish, given the complexity of the puzzle, the clues were easier for a cold solve.