Green’s Dictionary of Slang

a phr. used of someone who has a notably wide mouth.

c.1786		Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Fire Shovel. He or she when young, was fed with a fire shovel; said of Persons with wide mouths.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn) n.p.:
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1869		Notts. Guardian 18 June 3/5: Such conduct was more worthy of these who were 'dragged up by the hair on the head and fed with a fire-shovel' than of a gentleman.
c.1900		Harry Champion ‘What a Mouth’ 🎵 What a mouth, what a mouth / What a north and south / Blimey what a mouth he’s got / Well when he was a baby, aw gawd luv ’er, / Well his poor old Mother used to feed him with a shovel.