Thanks Gary.
It is a crude solution but one I have had to use. I have made an uncategorized category with zero weight and put all the assessment items I have not set yet (hidden items) into it.
This took about 15 minutes as after each one the screen has to completely refresh. Multiple moves would be much appreciated in the grades category screen. Anyway it is done now.
Please developers can you get a "Aggregate only visible items" option into the grade book. Using this current setup I have to unhide an item on the course screen so the students can see it, then open the item to modify it, and recategorised it, then get into the grade book and make it visible there as well. This seems a bit silly really. Then when I start my course next year I'll have to move all the items into Uncategorized again and hide them all again or when students go to check their grades they see all 40 items rather than just the 5 I have set in the first topic.
There has to be a better way.