By Robert Baker BBC Sport

Boxing promoter Frank Warren has hit out at Audley Harrison, calling on the British heavyweight hope to fight national champion Danny Williams.

"It's time for Harrison to put up or shut up," said Warren on learning of the Olympic champion's next scheduled bout against American Rob Calloway.

"Why doesn't he fight Williams? He said he would be British champion within five fights, but he's not even fought for an area title.

Calloway fights on what is known as the 'Bum Circuit' in America Frank Warren

"That's because he's not fought over 10 or 12 rounds, and the public are being constantly conned by these absolute one-sided mismatches.

"If they go to one of his shows they think that's what boxing is all about."

Warren, a long-standing critic of the way Harrison's career has developed, told BBC Sport that that the quality of his opponents must improve.

"I've nothing against Audley as a person, but I've got plenty of complaint about the eight fights he has had so far in his career.

Calloway is a blown up light-heavyweight Frank Warren

"Not one of them has been good enough to be a main event, and he seems to be following the trend with his latest fight."

"Calloway fights on what is known as the 'Bum Circuit' in America," said Warren.

"All his wins are against opponents of with non-descript records, and if Calloway, at the age of 33, was a decent fighter he would have fought for a recognised title by now - and I would have heard of him."

"Added to that he's a blown up light-heavyweight."