The new suspect being hunted in connection with the disappearance of Madeleine McCann is a "highly significant person of interest" to the investigation, the family's spokesman said today.
Clarence Mitchell refused to confirm or deny that the woman, described as a Victoria Beckham lookalike, had asked a British man: "Have you got her? Have you got the child?"
But he said it was right to identify the woman as a possible accomplice in the abduction of Madeleine.
Private detectives released an e-fit of the woman, described as glamorous and stylishly dressed, yesterday. They said she spoke with an Australian or New Zealand accent.
The conversation with the British man, who has not been named but is a married 41-year-old professional without children, is said to have taken place at a marina in Barcelona, Spain, three days after the youngster disappeared from Portugal.
Speaking on GMTV, Mr Mitchell said: "This is potentially a highly significant person of interest to the investigation. I can't go into any more detail.
"This woman is formally not accused of anything."
But he said reports identifying her as a potential "accomplice" were "right to identify that aspect of the story".
Appeals have been made in Australia in the hope of attracting further clues but Mr Mitchell admitted the whereabouts of the woman were unknown.
"We're not even absolutely sure she is in Australia," he said.
Mr Mitchell said Kate and Gerry McCann, Madeleine's parents, remained cautious about the new development.
"They have learned through bitter experience to neither let their hopes go up or down," he said.
But he said they had "drawn strength" from the new momentum in the investigation.
Mr Mitchell said the source of the information had been "checked out" and stressed there were "good operational reasons" for not disclosing exact details of the evidence.
"We specifically have not revealed the contents of the conversation this woman had with the new witness for good operational reasons," he said.
"The papers, of course, were going to speculate, we knew that. I'm neither going to confirm or deny that those quotes were in that conversation but it's potentially significant. What she said needs to be highlighted for the investigation."
Mr Mitchell said it was not known exactly why the new witness had waited until now before coming forward.
"That's a question that only he can really answer," he said. "He has told the detectives it was for personal reasons. They respect that. They've checked him out.
"He is a respectable businessman in his early 40s. He felt it was important. We understand he has grappled with his conscience to a certain extent but we are grateful to him for coming forward, even though it is so late."
Investigators said it was possible that Madeleine was smuggled hundreds of miles from the Algarve to Barcelona by yacht.
Former UK detective inspector Dave Edgar, who is leading the McCanns' private investigation, said it was a "strong lead" and appealed for information about the woman.
Madeleine was nearly four when she went missing from her family's holiday apartment in Praia da Luz in the Algarve on May 3 2007 while her parents dined with friends nearby.
Just over 72 hours later, in the early hours of May 7, two British men saw the woman while on a night out in Barcelona's popular Port Olimpic Marina.
She was well-dressed but appeared agitated and kept walking up and down outside the El Rey de la Gamba restaurant-bar as if she was waiting to meet somebody.
One of the British men approached and spoke to her before she went into a bar next door where she had a heated conversation with a local in what seemed to be fluent Spanish.
The British man did not disclose his brief conversation with her until he approached the McCanns' investigators about six weeks ago.
The woman was last seen walking away in the direction of a local hospital and ferry and cruise ship terminals.
The main witness described her as "a bit of a Victoria Beckham lookalike" who was aged 30 to 35, slim, about 5ft 2ins and had short brown hair.
She was wearing expensive-looking blue jeans and a jersey top, possibly of a pastel colour.
Anyone who knows the woman is asked to call the McCanns' investigation team on 0845 8384699 or through firstname.lastname@example.org .