Hi Fiona. 

At the moment there isn't an option to hide inactive nominal codes. As a workaround for now you can rename the nominal code to 'Do Not Use' > save. If you then click Filter at the top of nominal codes > set it to read 'Where - Name - Is Not Equal To - Do Not Use' > click apply > close. That will hide them.

The make inactive tick box is something we can look to introduce in to the program going forward. I suggest you log this as a suggestion to improve our Sage Accounts software on our Ideas Community: communities.sage.co.uk/.../

To log your idea select Sage 50 Accounts and then Submit an idea.

Once logged, we’ll be able to use your idea and help us to shape your Sage software. Other customers will also be able to vote on your idea.