Solved How to trim postcode..

[Number11]

That means there is something dodgy in the criteria of your query, not the function.

Can you copy and paste the entire SQL from your query - no editing?

Ok fixed it was because some of the data did not have a postcode so blank record fixed thanks for your help

 

[isladogs]

Ok fixed it was because some of the data did not have a postcode so blank record fixed thanks for your help

Makes sense.
I'd just tested your expression against all 2.6 million UK postcodes & you'll be pleased to know that it worked in all cases!
Even the special case GIR 0AA worked as its postcode area is officially GI

Anyway. attached is the postcode area data exported to a spreadsheet. Its taken from a 2018 dataset so data like households & population will not be up to date.