I have started to pull things apart and am fixing as I go along. By this I mean:-

1. Air pump earth oxidised, therefore a potential bad earth. All cleaned up. Fitted a crinkle washer to ensure bolt and earth tag are fully bonded together. Tested and good earth point present. Cranked engine no P0410 code set.
2. Air pump power connector oxidised, again a source for poor contact. All cleaned up and refitted. Cranked engine no P0410 code set.

Been for a short drive, no P0410 code set.

Now moved onto the Vacuum Solenoid (item 13 on the air pump drawing). I appreciate that this may have nothing to do with the P0410 issue, but I noticed the power cable to this unit was blocking the "breather pipe" and also a hard foul on the engine body. Perhaps the reduced airflow into this unit is the issue or perhaps the cable has become damaged and is shorting out?