A Christchurch judge has described a couple's treatment of an elderly man as akin to torture

A man and his partner have been found guilty of neglecting his 90-year-old father and confining him in unhealthy conditions.

During a three week trial it's been revealed they locked him in a dark room and forced him to wear adult nappies and a wet suit overnight, in case he soiled himself.

Judge Mark Callaghan says the son was an unbelievable witness, with inconsistencies throughout his evidence.

The couple were denied bail and will be sentenced on October 11.