Kate McCann could be charged with the accidental death of her daughter, according to a family member.

Philomena McCann told Sky News that police have suggested Kate killed Madeleine by mistake.

Madeleine's aunt dismissed the allegations and insisted Kate was innocent.

She said: "I have never heard anything so utterly ludicrous in my entire life."

Kate has been made a formal suspect in the case, a family friend said.

Portuguese police suggested to Mrs McCann that traces of Madeleine's blood were found in a car the family hired 25 days after the girl went missing.

She told them there was "no way" her daughter's blood could have been found inside the vehicle, the friend said.

However, her lawyer, Carlos Pinto de Abreu, warned her she could be charged today.

Madeleine's father Gerry is still being treated as a witness.

The McCann family spokesperson Justine McGuiness said: "The police are treating Kate as if she is involved in the death of her daughter.

"That suggestion hasn't been put to Gerry, so they are treating them differently.

"It is a ridiculous suggestion."

The McCanns announced on August 31 that they would take legal action against a Portuguese newspaper which claimed they killed Madeleine.

A large crowd whistled and shouted as Kate arrived back in Portimao for more questioning.

Mrs McCann was greeted by journalists, locals and holidaymakers, many of them whistling and shouting at her.

One British tourist shouted: "We believe you, Kate." But there were apparent jeers from other people in the crowd.

Madeleine's mother has been made an "arguida", a formal suspect, in the case, according to her friend.

An arguida receives more protection under Portuguese law, including the right to remain silent in formal interviews.

Sky News Crime Correspondent Martin Brunt said: "The police are doing this so they can ask her a list of 22 questions about the night Madeleine disappeared."

"There are specific questions they need to ask and they can only do that if she is a suspect."

The friend added: "She is shocked and surprised in several ways. First of all that such an accusation could be made against her.

"And obviously she is concerned that such a line of investigation can become a distraction from further attempts to find Madeleine."

Gerry McCann is due to be re-interviewed this afternoon.