Green’s Dictionary of Slang

to tell lies or ‘stories’; thus sprucer n., a liar or one who exaggerates.

1921		N&Q 12 Ser. IX 347: Spruce (To). Deceive; lie.
1925		(con. WWI) Fraser & Gibbons Soldier and Sailor Words 267: Spruce: To lie. To deceive.
1938		J. Curtis They Drive by Night 102: Garn. You’re sprucing. You got me figured out and weighed up.
1943		M. Harrison Reported Safe Arrival 7: A fly bloke what’s sprucin’ us he’s posh.
1980		Barltrop & Wolveridge Muvver Tongue 89: A specialist in tall stories is a ‘sprucer’.
1989		J. Morton Lowspeak 96: Madam – to tell lies; from the rhyming slang Madam de Luce = spruce (fib).