Assign Key to Spaces - Desired Option Not Available

Dear All,

I have just recently had to do a full reinstall of my OS, and to avoid corruption I couldn't just do a simple migrate. As such, many of my old preferences have been lost.

One issue for which I cannot find an answer concerns spaces. I originally set this up a long time ago when spaces first came out. I originally had it so that there were 4 spaces, and I could navigate between them by pressing COMMAND + 1/2/3/4. In the Mission Control Preferences of System Preferences I can't figure out how to make this an option.

Would anyone have any advice on how I might organise this?

Best,

Tony