The three judges scored the contest 116-113, 113-114 and 116-112 to Williams, an unexceptional journeyman whose claim to fame rests mainly on beating the burnt-out Mike Tyson in July last year.
Olympic gold medallist in Sydney in 2000, Harrison was unbeaten in 19 previous professional fights but had been criticised for the quality of his opposition and looked deeply unimpressive.
Billed as the biggest all-British heavyweight clash since Frank Bruno was beaten by Lennox Lewis at Cardiff Arms Park in 1993, the fight for the vacant Commonwealth title offered little to justify the hype or comparisons with the past champions. With boos, whistles and chants of 'What a Load of Rubbish' echoing around the ringside after nine dire rounds, it came alive only from the 10th when Williams landed a solid right hook to send Harrison to the floor.
Harrison came right back in the 11th however, stunning Williams with a left uppercut.
"Audley was dreadful," said former featherweight champion Barry McGuigan. "He told us he was the real deal. Nonsense, he's not the real deal, that was a terrible performance and Danny Williams deserved to win."
"Audley ran like he was petrified."