Here are the words they sing, as listed on their website:

5. 'WARE OUT MOTHER (trad)
Nightmares, Mother had, of navvies in the cellar
And dark eyes looking through the window outside
How we used to vex her, how we used to taunt her
How we would laugh and chant to her dismay

'Ware out Mother there's a navvy in the cellar
and two more looking through the window outside

Mother heard there was to be a river builded
Just a stone's throw away from the window outside
How we hugged each other, as we told our mother
"It's a canal, there'll be navigators too."

We told Mother there'd be barges full of jewels
And wondrous things past the window outside
But where's this river from? we said it flows from China
"Woah" thought Mom, "there'll be alligators too."

One night Jimmy led the navvies into town
and they looked like beggars through the window outside
There were navvies in the ale house, arguments and street fights,
Mother was delicate, she stayed in bed all week

One night Jimmy had a gentle way with words
and more pairs of hands than was decent, alright.
"Will you come along, me saucy little Susie,
Just let me put a few arms around your waist."

Soon our mother saw the navvy with her daughter
and she locked her up in the cellar downstairs
"Do you come along, me naughty filthy hussy,
Else I'll put this stick about your back."

Jim gave a wink, or it might have been a blink,
and he organised a tunnel 'neath the window outside
Not a body saw them, then they struck foundations
"Right" thought Jim, "I shall blow little hole."

Muffled bang, and there was dust and rubble everywhere
And Jim was in the cellar of his Susie once more
How they hugged each other, yet no-one told our mother
She still has her dreams, yet she's never learnt the truth.