use the symmetrical aspect - so place 4a on the top row, starting in 4th square along, then place 44a in corresponding symmetrical place on bottom row (top left corresponds symmetrically to bottom right etc). Then try and place in some of the down clues on the top row, etc.
Come back if you need more help
As always, many thanks Daniel. The preamble states that the eight central bars have to be clearly indicated. Am I right in assuming that all the other bars must be entered as well given no instruction to the contrary?
The preamble here seems to miss an important word, as any standard Spectator crossword grid is symmetrical whichever side is uppermost, with the plane of symmetry alternating between diagonals. This one is unusual because it exhibits fourfold symmetry, so the grid is identically symmetrical whichever side is uppermost, plane of symmetry about both diagonals.