Private investigators hoping to question a convicted paedophile over the disappearance of Madeleine McCann have returned to Britain empty-handed.

Gerry and Kate McCann's investigation team had hoped to quiz Raymond Hewlett at a hospital in Germany yesterday.

However, when the 64-year-old, who has been jailed for sexually assaulting young girls, finally agreed to meet them, they were reportedly already waiting to board a flight to the UK.

Former detectives Dave Edgar and Arthur Cowley were unable to return to the hospital in Aachen, where Hewlett is being treated for cancer.

Yesterday, Hewlett said: "I have nothing to hide. I am willing to talk with them."

He is alleged to have been staying near the McCanns' holiday flat in Praia da Luz, Portugal, when Madeleine went missing in May, 2007.

On Monday, Clarence Mitchell, spokesman for the Rothley family, had issued an ultimatum to Hewlett demanding he meet the investigators by yesterday morning in order to "eliminate him from the investigation".

In the wake of yesterday's events, Mr Mitchell welcomed Hewlett's willingness to cooperate and said an interview would be arranged.

He said: "The investigators are pleased to hear that Mr Hewlett has agreed to speak to them. He has again denied any involvement in Madeleine's abduction, and if it helps to eliminate him from the private investigation, then he has done the right thing by indicating that he will speak to the investigators.''

Alan and Cindy Thompson told a newspaper they met Hewlett while on holiday, and said he was living with his wife and six children in a converted Dodge truck, travelling from campsite to campsite around the Algarve and Spain.

Hewlett allegedly told the Thompsons he was approached by some "Gipsy tourists'' offering to buy his daughter, just before Madeleine went missing.

They also recalled him mentioning a "business'' trip to Morocco, where there were several alleged sightings of Madeleine.

Hewlett is said to have told the Thompsons he was at a market in Fuseta, 30 miles from Praia da Luz, when Madeleine vanished, they said.