French police are treating the case of a missing Sussex aristocrat as murder.

The news came as the Earl of Shaftesbury's family spoke for the first time and admitted: "We fear the worst."

In a statement, the earl's son Anthony Ashley-Cooper, 27, said: "My family and I are extremely concerned about the disappearance of my father.

"We have visited the French investigation in Nice and are convinced everything that could be done to ascertain my father's fate is being done.

"We remain in close contact with the police and will continue to assist in every way we can."

Mr Ashley-Cooper, one of two sons, lives on the family estate in Wimborne, Dorset, and added: "We will not be making any further public comment and ask that our privacy be respected at this difficult time."

The earl, 66 and married three times, was renting a flat in Adelaide Crescent, Hove. He has been missing for six weeks and was last seen leaving a hotel in Cannes on November 5.

French police later recovered a painting and pieces of furniture he reported had been stolen from him.

The earl had also told police he was assaulted in France after accusing four people of stealing antiques from his home.

Sussex detectives flew to France with information about the missing playboy but their involvement in the search has now ended.

Detective Chief Inspector Adam Hibbert said: "Our French counterparts are now treating the earl's disappearance as murder, although no body has been found."

Lord Shaftesbury had travelled to France to seek a reconciliation with his third wife, Jamila Ben M'Barek.

The earl had also been engaged to nude model Nathalie Lions after meeting her in a lingerie shop in Geneva. He is said to have broken off the engagement and had been involved with a nightclub hostess called Nadia.

Neighbours in Hove hoped the earl was in hiding with a girlfriend in a remote location but one said: "It is too long a time gap. He would have got in touch by now."

Sussex Police are liaising between French police and the earl's second wife and two sons.

Lady Shaftesbury and her son Anthony joined police on their recent trip to France.

At yesterday's Press conference, Detective Sergeant Paul Sellings said: "This is an extremely distressing time for the earl's family and friends."

Mr Hibbert said the "total lack of communication" from the earl had led police to suspect he had been murdered.

The earl's bank and credit card accounts had been checked, he said, and nothing untoward had been found.