I asked on the Scots-L Traditional Music list, and this is the answer which came back:

Date: Wed, 08 May 2002 22:59:38 +0000
From: Celtic World <celtic_world@hotmail.com>
Subject: Re: [scots-l] When the Battle's O'er - Pipe Tune

The composer of (When) The Battle's O'er (aka After The Battle) is Pipe Major William Robb, Argyll & Sutherland Highlanders late 1800s. The words were indeed by Andy Stewart.

Bruce Campbell
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