@Matt just at a corporate IT level. Thanks for pointing out how to access this feature. It will add to my list of reasons why we should be using the current LTR at least.

Have you changed the paths to match your install?

Worked it out in the end. Had to use "LOCALITY" not in (attribute(@atlas_feature, 'LOCALITY')) with an else statement that had no symbology. Then in the Atlas clip I had to exclude this layer from clipping.

I just tried both options and there's no error but when I cycle through the maps, I see no difference. Is it possible to use something similar in the filter?

For both I get an error like the following. This is in the Filter expression. ` - An error occurred when executing the query. The data provider said: OGR[3] error 1: SQL Expression Parsing Error: syntax error, unexpected $undefined. Occurred around : "LOCALITY" != @atlas_feature ^`