OK I've answered my own question. I downloaded the plugin and after some dicking around got it to work and I like it.
So for those who may follow here's what I've done.
Obviously download the plugin as per instructions
In the editor press F6 and enter this
Into the text box. Note that I like to auto save before the compile (npp_save) and that it seems you have to do the CD so make executes in the correct folder. Also I often work on 2 projects at the same time but in different folders so this is important to me.
This seems to work well, I swap to a different source file in a different tab (and folder), hit CTRL-F6 and it picks up the local makefile. So far so good.
Now I'd like it to highlight the errors and make them clickable. I believe you do this in the "highlight" dialogue (SHFT-F6), I enter
which is supposed to highlight errors and even make them clickable to go to the error line. So far I haven't got this to work.
Also the console takes up a lot of the editor window but you can just grab it and move out of the editor so it's a separate window, good if you have a large screen.