Alan, the version I have is the one sung by John Foreman, The Broadsheet King, as written by Sidney Carter - hope it helps.

DOWN BELOW
(Sydney Carter)

When you're working in the dark, down below
Underneath St James Park, down below
When you're working in the dark
Underneath St James park
It isn't half a lark, down below

Now it isn't hard to tell,down below
If it's Bow or Clerkenwell, down below
Cos Bow and Clerkenwell
Have a different kind of smell
And you know it pretty well, down below

Come down Covent Garden way, down below
in the merry month of May, down below
The fragrance of the flowers
Gives us many happy hours
And we sing a roundelay, down below

When to Billingsgate you come, down below
When to Billingsgate you come, down below
When to Billingsgate you come
Well the things begin to hum
And the smell will knock you dumb, down below

And the objects that you find, down below
Serve to exercise the mind, down below
There are watches that wont wind
All wrapped up in bacon rind
And that isn't all you find, down below

Yes there's something in a sewer, down below
Seems to have a strange alure, down below
The magic of the drains
Is a thing I can't explain
But it's calling me again, down below
Yes it's calling me again, down below