The woman who murdered Coulsdon student Meredith Kercher has launched an appeal against her conviction.

Lawyers for Amanda Knox, who was jailed for 26 years in January for the murder of Miss Kercher, have submitted a 300-page document calling in to question DNA evidence used to convict the 25-year-old.

The appeal also attacks what is described as contradictory evidence given by chief prosecutor Giuiliano Mignini during the year-long trial, as well as the circumstances under which Knox made a confession to the police.

Mr Mignini initially claimed Miss Kercher was murdered because she refused to take part in a drug-fuelled sex game, but also claimed Knox and her boyfriend Raffaele Sollecito killed because they were driven crazy by powerful narcotics.

He also said robbery was the motive before suggesting Knox murdered her house-mate because they did not get on.

Defence lawyers decided to appeal after independent forensic experts raised concerns over how the 480 pieces of evidence were collected and dealt with by police.

Knox was connected to the murder scene through a miniature piece of DNA found on a knife chosen at random by a police officer from a kitchen drawer, while Sollecito was convicted because of DNA found on a bra-clasp on the bedroom floor.

The defence say the latter, which was ignored by investigators for more than six weeks, was moved around the bedroom floor after the murder and could have become contaminated.

Miss Kercher’s was body was found with a cut throat in the bedroom of the cottage she shared with Knox on November 2007.

Knox and Sollecito claimed they were not at the flat on the night of the murder, while Guede originally said an intruder had broken in to commit the crime while he was listening to music on the toilet.

The move comes just two days after Italian prosecutors launched their own appeal to get Knox and Sollecito’s sentences increased to life terms.

Ivorian drifter Rudy Guede was jailed for 30-years for his part in the murder following a fast track trial last year.