Where does the phrase "'ecky thump" come from?

Ecky thump is the old Lancastrian (Lancaster, England)
Martial Art. It was made known to a worldwide audience
through its reference by Monty Pythons Flying Circus.
Somewhere up north
up north.. it means: oh dear!! or for gods sake.!!..
The Goodies, an old Comedy Series from the 70's featuring Bill Odie
The Goodies (goody, goody, yum-yum).

Ee bah goom, it's a long time sin' ah heeard that!

#42 Kung Fu Kapers
AKA Ecky-Thump (g)
Series Five, Programme Seven
1st BBC Transmission: 24 March 1975
BBC Project Number 98447

Bill reveals he is a master of the ancient Lancashire martial art of Ecky-Thump. The effectiveness of Ecky- Thump leads to a craze sweeping the nation, which Bill intends to exploit by taking over t'Parliament. The only way to stop him is by adding remote control his secret weapon - black puddings.

Guest Cast
Michael Barratt
Richard Pescud
William F. Sully
I think Flying Circus also used it.

It is, indeed, an expression of surprise - maybe from 'By Heck!' with the 'thoomp' added for emphasis, like.

The School of Ecky Thump was in Rochdale.
I think The Goodies made it up. It was a sort of Northern English kung fu.
It does come from the Goodies but they didn't make it up. One of them came from somewhere foreign like Yorkshire I think and they used the phrase there.
When that particular episode of the Goodies was broadcast, a Glaswegian man actually died laughing. He'd been in poor health, and when Graham Garden bounded in wearing a kilt and failing to play the bagpipes, jigging and reeling in speeded-up motion, swiftly to be dispatched by an unimpressed Lancastrian Bill Oddie with a large black pudding, this viewer couldn't take any more and had a heart attack. His family were happy that he went out on a good note and wrote to thank the Goodies.