The parents of Madeleine McCann have successfully argued for a speedy hearing in their dispute with a retired lawyer they say has mounted a libelous harassment campaign against them.

Gerry and Kate McCann, of Rothley, are asking the High Court to jail 65-year-old Tony Bennett, who they say has persisted in spreading false allegations against them, both on-line and in print.

Mr Bennett, of Harlow, Essex, promised in November 2009 to stop making allegations that the couple were guilty of, or suspected of, causing their daughter's death, disposing of her body and trying to cover up what they had done.

Mr and Mrs McCann's lawyers claim he has since breached that formal undertaking more than 150 times and are seeking his imprisonment, or other punishment, for alleged contempt of court.

At the High Court yesterday, Mr Justice Tugendhat underlined the vital importance of court orders and undertakings being obeyed and directed that the couple's case against Mr Bennett be heard "as soon as practicable".

Mr Bennett is asking the court to vary the undertakings he gave in 2009 so that he can publish to the world at large what he claims is "credible evidence" that Madeleine died in her parents' holiday apartment, that her parents have covered this up and have, on occasions, lied about matters connected to her reported disappearance.

The McCanns "deny that there is any truth in any of the allegations which Mr Bennett wishes to be free to make" and argue that his continued publication of "numerous grave and actionable libels" against them amounts to harassment.

Madeleine went missing in May 2007 from an apartment complex in Praia da Luz, Portugal, where her parents – both doctors from Rothley – had been holidaying with a group of friends.