Impotence was not a valid ground of appeal for a convicted sex attacker because it was something which affects 'all humanity' from time to time, the acting Chief Justice said yesterday. The 'delicate matter' was considered by three male judges before Kwok Ngai-man's appeal against conviction was rejected. Gerard McCoy QC, for Kwok, claimed the attacker's 'temporary incapacity' made it impossible for him to have even attempted to have sex with his 18-year-old victim. But Mr Justice Noel Power said: 'This is an incapacity from which all humanity suffers from time to time. It does not mean anything.' Kwok, who was under the influence of drugs at the time of the attack, did succeed in having his sentence reduced by a year. Kwok, 23, was jailed for 13 years in August by Mr Justice Raymond Sears who said he deserved no mercy after being convicted of attempted buggery, robbery and burglary. He had heard how Kwok forced his victim to strip after he broke into her home, beat up her mother and tied up her 13-year-old brother. Mr Justice Sears later backdated the sentence to begin from Kwok's arrest a year earlier. That was ruled invalid but the appeal judges cut the sentence by a year.