eleven, n. — Green’s Dictionary of Slang

eleven n.

[from the film Spinal Tap (1984) where a guitar amplifier’s volume knobs are marked from zero to eleven, instead of the usual zero to ten; note Aus. milit. cadets’ contemporaneous eleven, ‘an attractive woman who is prepared to fellate and swallow the sperm’ Simes (2018)]

usu. in phr. turn (up) to eleven, to attain an absolute extreme.

[1984		‘Nigel Tufnel’ in Spinal Tap [film script] ‘It’s very special because, as you can see, the numbers [on the amplifer] all go up to 11’].
2018		Secret Barrister 296: [T]hey [Parliament] looked at the list, turned (a) [sic] up to eleven and to tabloid joy introduced mandatory minimum sentences.
2020		‘Secret Barrister’ Fake Law 268: [S][he was simply riffing on a theme composed and turned up to eleven by the preceding Labour Government.