I found an article titled "We All Just Knew Her as Ruby" at http://www.mustrad.org.uk/articles/ruby_c.htm. The page has these lyrics:

Down by the Old Millstream (Nuts in May)

This song, above all others, is the one recalled by everyone contacted in this project.  Similar versions are known to exist and can be found on internet sites; I heard something similar shortly after learning the same in the Anchor at Sidmouth in around 1981.  The verses are spoken, with the exception of the lines leading 'down by the old millstream' which is sung, with the second line acting like an interrogation from the audience (e.g. roses??) to which the singer replies in confirmation (e.g. roses!)

[Chorus]
Let's go out tonight, tonight,
The moon is shining bright tonight.
I see a twinkle in your eye - aye aye aye
Everybody's watching us, they're watching you and I
Let's go round the corner and have a bit on the sly
Aye aye, tiddly aye aye aye .  .  .

He took her gathering nuts in May,
Nuts in May? Nuts in May!
Down by the old mill stream, aye aye aye
But instead of gathering nuts in May
He put her in the family way
Down by the old mill stream.

[Chorus]

He took her gathering roses,
Roses? Roses!
Down by the old mill stream, aye aye aye
But instead of gathering roses
He took off all her clotheses
Down by the old mill stream.

[Chorus]

He took her gathering watercress,
Watercress? Watercress!
Down by the old mill stream, aye aye aye
But instead of gathering watercress
He got her in one hell of a mess.
Down by the old mill stream.

[Chorus]

He took her to see his mother,
His mother? His mother!
Down by the old mill stream, aye aye aye
But instead of seeing his mother
They had a bit of the other
Down by the old mill stream.

[Chorus]

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Here's a recording sample: http://www.horntip.com/mp3/fieldwork/horntip_collection/g/steve_g/2006-03-05/Down%20By%20The%20Old%20Mill%20Stream%20[Learned%20Early%201960s].mp3