AndyG, here are two verses from M. Pollard, Ballads and Broadsides, of a song titled (how else?) Plains of Waterloo:

Come all courageous Britons brave, of honour and renown,
who fight for King and country, likewise for Britain's crown,
I'll tell you all the story, as far as I do know,
concerning the great victory that was gained at Waterloo.

...
The tune had not been half played out till the French had danced their fill,
twenty thousand of her bravest troops upon the field lay still
. Ten thousand prisoners we had, with Imperial eagles too,
and British vioctory was proclaimed on the plains of Waterloo.

Well, that's the first and the before last verse of a song too long to type today but I wouldn't mind the work if it's the right song. It sounds like it could be the song you had in mind. I have never heard it and my source gives no tune.

Wolfgang