In track view tracks 1 to 31 have disappeared leaving tracks 32 on visible i can still hear tracks 1 to 31 and can see them in the console Where have they gone and how can I get them back? I need to draw envelopes on them.

Sounds like you've hidden them with the track manager. Press H and check them there or SHift + H to show all

Spot on Thanks How did that happen i wonder?

Inadvertent shortcut press maybe. Hide tracks is Ctrl+ H or show only selected tracks Ctrl+Shift+H

Twigman - I use H a lot. 

I tend to keep checked only the tracks I want to see at the particular moment. Track folders are great to collect tracks and to collapse them away from view when you're not presently working on tracks in a particular folder.
In addition to track folders, I've found to that I also benefit greatly from using H to hide/show tracks and/or track folders.

I find it convenient to use H. By hiding tracks and folders which I don't need to see at the moment I've found that I stay better focused on working on the tracks that I need to. 

H helps get rid of distractions and lets me work more efficiently.