A millionaire widow and her socialite daughter, whose £6m luxury yacht has been linked to the latest clue in the Madeleine McCann hunt, have offered to help.

Rhonda Wyllie, 52, and Melissa Karlson, 31, said they would do all they could to help Kate and Gerry McCann's detectives.

Their yacht, Willpower, was spotted in Barcelona's Port Olimpic marina on May 6, 2007 – three days after Madeleine's disappearance.

They insisted they were not in Barcelona at that time.

A Wyllie Group spokesman said: "Rhonda and Melissa are perplexed by the media coverage of the past 24 hours, especially given that neither of them was in Spain on the night in question."

Willpower was alleged to have been moored at Barcelona at about the time a woman, with an Australian accent, reportedly asked a British man if he was there to deliver her "new daughter".

The McCanns' private detectives last week launched an appeal for information about the mysterious woman, described as a Victoria Beckham lookalike.

Relatives of the Australian socialite said she would do all she could to help the worldwide hunt for the missing child.

Her brother, Wayne McGrath, said: "I have spoken to my sister and she is devastated. She doesn't know anything about this.

"She is happy to co-operate with and help any investigation."

The McCanns' spokesman Clarence Mitchell said the investigators were ready to travel to Australia at short notice.

"If anything urgent happens and they need to go to Australia quickly, they will. But they're not on the verge of setting off," he said.

There is no suggestion either of the women, or any of their yacht crew, had anything to do with Madeleine's disappearance.

Madeleine, of Rothley, went missing from her family's holiday apartment in the resort of Praia da Luz, in Portugal, on May 3, 2007.