That makes sense thank you, if I highlight changes as i go I can also then refer back and report to each reviewer "re comment x; please see line (new line numer)"

I'm going to merge their comments now and sort them so I can work backwards rather than going just going through reviewer by reviewer.

Thanks again, that lets me get on with it... in the meantime though, if anyone does think of a way to actually preserve the old numbering, (possibly even beside the 'new' line numbers which update as you edit) it's still bugging me!