I found a solution for MY problem but it would be great for most.
As I am on a Mac I istalled less.app ( http://incident57.com/less/ ), it uses less.js to compile the less for you. As of a couple of days ago they added a new feature:
NEW FEATURE: "backwards @import parsing." If you have a file, X, that imports another file, Y, and you make changes to Y, X will now automatically recompile when you save Y (if auto-compile is on). This feature is automatic; there's nothing to turn on or hook up. You'll see "triggered by: X" in the compiler result when it happens.
Turns out it works very well indeed. Hope this helps someone!