As the origins of the phrase itself, I believe it was a sanitised version of (excuse the language) "I'll go to f**k" to express one's surprise or disbelief.

Much like phrases like "shut the front door". Replacing the expletive with a similar sounding word. Often for comedy effect, with a well mannered audience expecting the expletive and preparing to reprimand the utterer only to have the offending word replaced.

I'm from West Yorkshire and I can testify to this phrase being still in use in both its original and sanitised versions today.