A battle is being waged over the copyright of the diary of Anne Frank.

According to European copyright law, work passes into the public domain 70 years after the author’s death, which, in the case of Anne Frank, is January 1 2016. This means that other publishers could produce versions of the famous diary about a young girl hiding from the Nazis in a secret annex of a house in Amsterdam.

However, the Anne Frank Fonds – the Swiss foundation that currently holds the copyright – has warned off anyone preparing to publish it next year and is trying to extend its lease on the diary by adding Anne's father, Otto Frank, as a co-author. Otto Frank died in 1980 so copyright in his name would persist until 2050.

According to the Fonds, Otto's work "editing, merging and trimming entries" legally makes him a co-author because they “in effect created readable books from Anne Frank’s original writings”.

However, this co-authorship is being contested in court by the Anne Frank House museum in Amsterdam, which has been planning to release an online version of the diary to correspond with the copyright expiring.

The Anne Frank museum is not affiliated with the Anne Frank Fonds, despite both having the support of Otto Frank, who bequeathed different materials to each organisation.

A spokesman from the Anne Frank Fonds said that extending the copyright will protect the young diarist, making sure that “Anne Frank stays Anne”.

However Annemarie Bekker, spokeswoman for the Anne Frank House museum, said: “Is Otto Frank co-author of the diary of Anne Frank? No, Anne Frank is the sole author of the diary … and the short stories. There is no co-author in these writings, not Otto Frank or any other person.”