Labor leader Bill Shorten was doing more than channelling Paul Keating in his hard-hitting budget reply speech on May 15 for which he received sustained applause from the public galleries.

He was relying directly on the former prime minister's expertise - and, in some cases even, his words.

Fairfax Media has been told the speech, the most important single oration Mr Shorten has made as leader, was workshopped with a wide variety of senior labour movement figures including several of his frontbench colleagues, former ACTU secretary Bill Kelty and, most crucially, Mr Keating - who advised on the final version.