The Appeal Court ruled that the fact that Angus Diggle, 38, of Bolton, Greater Manchester, had stopped the assault immediately his advances were spurned should have been held in his favour, in addition to his sexual and social naivety.
But Lord Justice Evans, sitting with Mr Justice Judge and Mrs Justice Bracewell, said that the sentence passed last September at Swansea Crown Court could not be reduced further because of Diggle's failure to plead guilty, forcing the defendant to repeat her evidence twice, and because he had shown no remorse.
His appeal against conviction, which turned on whether a damning statement made by Diggle to officers in a police car shortly after his arrest, should have been allowed, was rejected.
Diggle was jailed eight months ago after being convicted at the Old Bailey.
The jury had heard that Diggle, wearing only the frilly cuffs of his Highland outfit and a green condom, attempted to have sex with a 25- year-old lawyer from Edinburgh when she let him stay at a friend's flat after a St Andrew's Day ball in London. They were only due to stay a few hours before catching their trains home.
Shortly after his arrest Diggle allegedly told officers, 'I've spent pounds 200 on her, why can't a I do what I did?' as he was being taken in a squad car to Kensington police station in west London.
Richard Ferguson QC, for Diggle, argued that this evidence which had attracted great media interest should not have been allowed in evidence in the trial because the officers had failed to follow guidelines and it was prejudicial to the defence case. But that was rejected.
Lord Justice Evans said Diggle had shown no remorse and the trial judge had described the woman's experience in having to give evidence as 'a terrifying and degrading ordeal for her'.