What I've got so far, from my own (unreliable) memories, and questioning still more unreliable sources is:

All of a sudden
A bloomin' Black Pudding
Came sailing through the air
All of a sudden
A bloomin' Black Pudding
I really do declare.

It missed my mother
And hit my brother
And knocked him off his chair
Did he duck?
Did he fuck -
It hit him fair and square

Me nanny went crackers
And stamped on his knackers
And pissed against the wall
The dog went mad
And bit me Dad
In his one and only ball.

It sounds like there's still more of a story to come, but that's all I've been able to find - most of it, in various forms, has already been posted, but surely there should be more?