While the use of narrow confinement to inflict stress-position torture is well documented - the Tower of London's "Little Ease" cell is occasionally cited by name in the Calendar of State Papers, although the actual cell used has been lost to the centuries of alterations and repairs since it was last used and nobody's even sure where it was now - the idea that someone could endure twenty years of it seems somewhat implausible.

In case it helps someone, the cited article says that the Abbey was closed and turned into a prison after the French Revolution ... and the prison was closed in 1863.