The speculation about what could possibly have happened to the 4 year old daughter of two most respectable doctor parents and model citizens has been little short of phenomenal, but the latest theory and speculation is about to hit home the hardest and Kate and Gerry McCann will face their toughest questions yet.

The latest accusation from Portuguese Police is that Madeleine McCann fell and hit her head so hard, she died instantly from a brain injury.

Police believe that Kate and Gerry panicked through fear of being arrested and charged with murder and being kept in Portugal and imprisoned.

It is strongly suggested that  Madeleine McCann died after falling down a flight of steps and that her parents hid her body because they feared being blamed.

It was alleged that the four-year-old smashed the back of her head on a ceramic flagstone at her family's holiday apartment in Praia da Luz.

Kate and Gerry McCann then got rid of the body, possibly with the help of their friends, this latest theory against the couple, who are official suspects in their daughter's disappearance, was claimed by a source close to the McCanns.

Kate McCann has already said she would be willing to risk going to prison by speaking out about the events of May 3 in breach of Portugal's secrecy laws.

The couple are prevented from speaking about the investigation, and have expressed frustration that they are not able to defend themselves against increasingly lurid allegations in the world’s press regarding their daughter's fate.

In another twist, police are investigating claims that a disgruntled ex-employee from the Ocean Club, where the family was staying, may have been involved in Madeleine's abduction, but a source close to the investigation claims that the truth will out very soon..

Yesterday, the McCanns spent a quiet day in their home town of Rothley in Leicestershire, marking 150 days since their daughter disappeared.

They are adamant that she was abducted but police in Portugal were described as "100 per cent" certain that the little girl died in the family's apartment in the Algarve.

A senior detective told Portuguese newspaper 24 Horas: "The only thing to investigate is how the body disappeared." The newspaper claims Madeleine fell down steps at the back of the apartment. Photographs taken at the time show a children's safety barrier above the steps.

The new theory emerged after a report from Britain said specialist sniffer dogs had detected the "smell of death" on the steps, it was claimed. In the past, Mr and Mrs McCann, both 39, have been accused of hiding their daughter's body because she had been sedated.

But yesterday, a source close to the couple hit back at the allegations.

"Where is the proof that this happened? Madeleine was put to bed at 7pm and there was a witness. When is Madeleine supposed to have fallen?

"If the police are 100 per cent certain that Madeleine fell down some steps, that means they must be able to prove she died in that way. It's just not possible without a body."

The couple's spokesman, Clarence Mitchell, added: "It is just ludicrous. All of these reports are unsourced and unsubstantiated."

A tip-off claiming that a former Ocean Club employee was involved in Madeleine's disappearance was sent to the Prince of Wales's official website, and passed to police.

It alleged that a maid who used to work at the Mark Warner resort kidnapped Madeleine in revenge for being fired. Police have discovered the woman identified does exist and that the tip-off came from an email address registered in the Iberian peninsula.