Hi Sweep, thanks for the response. I tried yours as it looks the simplest (for me to understand anyway!)
It works fine with all variants except the old London ones (i.e. AN, ANN, AAN, AANN) for these, I get the following results; the 2 character one gives #Value! error, the 3 character ones have a space before the 1st character and the 4 character ones have a space between the 1st and 2nd characters.

This is probably my fault as I didn't refer to these short postcodes in my initial post - I was still chugging through test data - so sorry if I led you down the wrong road..

I had these variations in mind when I did my clunky version, but I also get a similar result except the 2 character one has a space before the 1st character.
Any mods to your code would be gratefully received as its easy for me to follow! Once again apologies for the lack of info.
Kind regds
Mike