Thanks for a quick reply.
Before going the external build script way, when the project specific build-script itself was self contained, I was using this plugin. Without it, the artefact was not getting published to remote repository.
Also, in current scenario (of using external build script without this plugin), the last task :publishMavenPublicationToInternalRepository is failing though settings.xml contain appropriate credentials.
May be I am missing some bit. Some more inputs would help.