The family of the late Labour peer, Lord Janner, have challenged the Independent Inquiry into Child Sexual Abuse’s plan to look into allegations against him.

Part of the inquiry is expected to look at claims against the former MP, but his family said the plan proved the probe was “being conducted on the presumption of guilt, contrary to the fundamental principles of British justice”.

Daniel Janner QC, Marion Janner and Rabbi Laura Janner-Klausner, met lawyers from the Inquiry on Wednesday to protest against their father’s inclusion in the long-running investigation.

Lord Janner was ruled unfit to stand trial on child sexual abuse charges in December 2015, and died shortly after.

In a formal submission to Professor Alexis Jay, inquiry chair, the family said: “Our late father was never convicted of any offence and died an innocent man.

“We take issue with the Inquiry’s underlying assumption of guilt," as evidenced by the words, "‘the Inquiry is encouraging all victims and survivors of child sexual abuse to share their experience’.”

They said the inquiry had totally failed “to acknowledge our late father’s good character and legal status as innocent.

“The wording is contrary to the common law presumption of innocence.”

Mr Janner said his father was “the only individual who is being mistreated like this”.

More than 30 people made claims against Lord Janner, with the alleged offences said to have taken place between 1955 and 1988. Lawyers for the alleged victims say their clients have been waiting years for justice.

But the Janner family has always strongly denied the allegations, and in the 12-page submission handed to Ms Jay, they presented the evidence they believe supports their father’s innocence.

“The late Lord Janner’s accusers are fantasists and compensation seeking,” said the family in a statement.

They added: “Key witnesses and accusations have already been discredited in the media and in the Scottish Crown Court, and the lies will be exposed when the late Lord Janner’s children fight them in the civil case.”

The family points out “when the most serious offences were said to have taken place” their father was abroad, suggesting it was physically impossible for them to be true.

They also argued alleged victims only decided to sue “after 2013, when our father had well-publicised dementia”.

The family has requested core participation status in the inquiry, giving them the right to make legal submissions, suggest questions and receive advance notice of the Inquiry’s report.

“If the decision remains to hold the strand, we hereby apply to address the Inquiry at the prospective March hearing date. Daniel Janner QC will do so on behalf of the family.”

In the submission the family added: “We have been treated appallingly by the Inquiry. Until now we only heard of dates of hearings and postponements in the media.”