An interesting but obscure word.

[MrsSeanBean]

Garn.

It is not particularly easy to find a translation for garn.

I hear see it as the sort of thing a 19th century ruffian might have said, but I feel it merits wider usage.

Can anyone help?

Means "yarn", does it? In that case it is of German origin, I think..

Round ere, that means 'not ere no more'.

OED:
Colloq. (chiefly Cockney) pronunciation of go on (see GO v. 86j), often used to express disbelief or ridicule of a statement.

1886 in H. BAUMANN Londinismen 62/1.
1888 J. RUNCIMAN Chequers 80 Garn, you farthin' face!
1914 G. B. SHAW Pygmalion 1, in Nash's Mag. Nov. 152/2 The Note Taker (whipping out his book). Heavens! what a sound!..Ahahahowowowoo! The Flower Girl (tickled by the performance, and laughing in spite of herself). Garn!
1922 ?R. CROMPTON? JustWilliam viii. 166 Garn! S'ours! We found it.
1925 Glasgow Herald 9 Jan. 8 He complained that if he used such words as ?garn? or ?struth? he was accused of vulgarity, whereas were he capable of imitating the peculiar sounds such as were heard from those north of the Tweed he would be able to move in any society.
1968 A. HOLDEN Death after School iii. 22 ?Garn,? called out someone, ?tell us somefing we don't know!?

MrsB, respect!!

[cuts]
[pastes]

[bows]

It's a merge between Gosh darned isnt it?

The Flower Girl (tickled by the performance, and laughing in spite of herself). Garn!