Green’s Dictionary of Slang

chamber of horrors n.

1. sausages [the supposedly dubious contents].

[UK]Farmer & Henley Sl. and Its Analogues.
[UK]Globe (London) 15 Feb. 1/5: Cheap sausages [...] ‘bags of mystery’ and ‘chambers of horrors’.

2. the Peeresses’ gallery at the House of Lords [‘its being railed round as if it contained objectionable or repulsive inmates’ (B&L)].

[UK]Barrère & Leland Dict. of Sl., Jargon and Cant.