Hi Luke,
That was an extremely fast response 
I’d seen the documentation on using buildSrc but had hoped to keep the codebases as decoupled as possible. I thought a multi project build setup might do the trick. Ah well, that’s a shame.
Could I setup the build script in the webapp project to check for the plugin jar and then throw an error if it’s not been built, otherwise include it in the build script classpath? So that I could use it within the build script with
apply plugin: "myplugin"