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The father of Tony Hudgell had 12 teeth replaced after being held hostage in his prison cell.
Inmates shouted that Anthony Smith should lose his legs - a reference to the appalling violence he inflicted on his son - during the two-hour ordeal at HMP Swaleside on the Isle of Sheppey.
Smith was serving a 10-year term for child cruelty after he and Jody Simpson abused Tony at a Maidstone flat.
Tony, now seven, lost both legs as a result of the injuries and his campaigning with adopted mum Paula led to a recent law change. Tony's Law could see abusers jailed for life.
Two prisoners took Smith hostage to force the authorities to move them away from the prison, Maidstone Crown Court heard.
They later claimed Smith had volunteered but he denied this.
Smith, from Whitstable, was pushed into his cell after collecting his breakfast and beaten up.
Maidstone Crown Court heard that Michael Stewart - who was serving 10 years for serious violence - and Nathan Odgers - who is serving 10-and-a-half for aggravated burglary - then barricaded themselves in after tying Smith to the bed.
A prisoner was heard to shout: "He should have his legs chopped off."
The two-hour ordeal happened in August 2018 - but it would take another 19 months before the CPS would authorise charges.
Now a judge has said the delay was "extraordinary and unconscionable" and cut their sentences by a year.
Stewart, 31, was given an extended jail term of eight years and five months and father-of-four Odgers, 36, received an extended sentence of nine years and six months.
Both men admitted charges of false imprisonment and assault.
Judge Jeremy Donne QC told how Smith needed 12 teeth replaced - although the pair were not responsible for all of the injuries.
He said he accepted the motive for the attack was not revenge but a desire to move to a different jail.
He ordered that Stewart serve an immediate jail term of three years and eight months and Odgers four years and six months.
The judge then ruled the two, will also have to serve another five years on licence when they are released after serving two-thirds of the jail terms.