Green’s Dictionary of Slang

O’Reilly n.

[O’Reilly was apparently a real person, poss. a trade-unionist on the Liverpool docks]

used as an intensifier in general excls. as below.

In exclamations

blimey O’Reilly!

a general excl., presumed to be an intensifier of blimey! excl.

[US]O.O. McIntyre New York Day by Day 5 June [synd. col.] The new song of the trenches is called [...] ‘Bli’me O’Reilly You Are Looking Fine’ [...] The chorus goes something like this [...] Gor bli’me O’Reilly, you are looking well.
[US]T.A. Dorgan Indoor Sports 8 May [synd. cartoon] [lyrics] ‘Blime me Mr Reilly, but you are looking well’.
[UK]F. Norman Dead Butler Caper 78: Blimey O’Reilly, it’s Partrick Tomlinson!
[UK]D. Mitchell Black Swan Green 64: Blimey O’Riley, this, this, is precisely the problem.
blind O’Reilly!

1. a general excl. of surprise, excitement etc.

[UK]‘Sax Rohmer’ Dope 139: ‘Eh?’ roared George. ‘Eighty quid! Eighty quid! Flamin’ blind o’ Riley! D’you think I‘m up the pole? Eighty quid? You’re barmy!’.
[UK]G. Kersh They Die with Their Boots Clean 54: Oh God blind O’Reilly suffering Christ Christ in Heaven above so help me!
[UK]C. Harris Three-Ha’Pence to the Angel 22: Blind O’Reilly! [...] Don’t all rush!
[UK]G. Kersh Fowlers End (2001) 212: ‘It does tick a bit, doesn’t it?’ ‘You spat a bootful, it ticks! Blind O’Reilly, I never ’eard such ticking.’.

2. used as an intensifier.

[UK]G. Kersh They Die with Their Boots Clean 120: Them barrels must gleam like Blind O’Reilly.
God blind old Reilly!

a general oath of annoyance, incredulity, etc.

[UK]G. Kersh Fowlers End (2001) 133: Well, Gord blind O’Riley! Sam Yudenow don’t ’alf pick ’em!
[Ire](con. 1940s) B. Behan Borstal Boy 11: God blind old Reilly if one of them could even name the bloody things.