Green’s Dictionary of Slang

flare up! excl.

also flare up and join the union!
[coined at the burnings that accompanied Reform Riots of 1832, esp. in Bristol]

a cry of delight, triumph or defiance.

[UK]‘The New Flare Up!’ in Flare-Up Songster in Spedding & Watt (eds) Bawdy Songbooks (2011) IV 279: The only word is Flare up. / A shocking hat, what are you at? / This fashions word will tear up / [...] / For lively kids and pats galore, / The classic word is flare up.
[Ire]Tipperary Free Press 23 Aug. 3/1: Come flare-up, and flare-up, me ould Mail boy, / The Orange gang are thronging forth, / The Prods are running from the North.
[UK]‘Ax My Eye’ in New Cockalorum Songster in Spedding & Watt (eds) Bawdy Songbooks (2011) II 25: I’ve a randy dandy, tear up, flare up, / Moke that cost me forty bob.
[UK] ‘Who Are You?’ in Bentley’s Misc. Jan. 88: Another passing me cried ‘Flare up!’.
[UK]C. Mackay Memoirs of Extraordinary Popular Delusions (1869) 242: Its successor enjoyed a more extended fame [...] This phrase was ‘Flare up!’ and it is, even now, a colloquialism in common use. It took its rise in the time of the Reform riots, when Bristol was nearly half burned by the infuriated populace. The flames were said to have flared up in the devoted city. Whether there was anything peculiarly captivating in the sound, or in the idea of these words, is hard to say; but whatever was the reason, it tickled the mob fancy mightily, and drove all other slang out of the field before it. Nothing was to be heard all over London but ‘flare up!’ It answered all questions, settled all disputes, was applied to all persons, all things, and all circumstances, and became suddenly the most comprehensive phrase in the English language.
[UK]H. Mayhew Great World of London I 44: These would be succeeded by cries of [...] ‘Flare up my never-sweats’.
[UK](con. 1830s) H. Vizetelly Glances back 103: No end of unmeaning slang phrases [...] were in circulation liming the multitude and the ‘faster’ section of society. One’s ears were incessantly assailed with such cries as ‘What a shocking bad hat!’ ‘There he goes with his eye out!’ ‘How are you off for soap?’ Flare up! and join the union,’ ‘Does your mother know you're out?’ or ‘It’s all very fine, Mr. Fergusson, but you don't lodge here.’.
[UK]G.A. Sala in Daily Tel. 28 July in Ware (1909) 133/2: ‘Flare-up’ at the present time is a purely jocular interjection. A noisy revel is very often spoken of by bacchanalians as ‘a jolly flare-up, but sixty-three years ago ‘flare-up’ had another and a very sinister signification. To it was added the admonition ‘to join the Union’. ‘Flare-up and join the Union!’ The Union part of the cry is associated in my mind with processions of working men, yelling and cursing and bearing banners embellished with death’s – heads and cross-bones, and inscriptions about ‘Bread or Blood’; while ‘flare-up’ had a direct bearing on incendiarism.