They will work with British detectives and plan to search the house of victim Saad al-Hilli in Claygate, Surrey.Officer Marc de Tarle was first to land at Heathrow, and three colleagues were arriving last night and today.

Investigators also disclosed that Mr al-Hilli's brother has approached UK police to deny any feud with his sibling over money.

Iraqi-born Mr al-Hilli, 50, was gunned down in his car alongside his dentist wife, named by neighbours as Iqbal, while on holiday in the French Alps.

An older Swedish woman, who was travelling in the car, was also killed, along with Sylvain Mollier, 45, a French cyclist who apparently stumbled across the attack in Chevaline.

The couple's four-year-old daughter Zeena lay undiscovered under her mother's corpse for eight hours after the murders, while her seven-year-old sister Zainab remains in a medically induced coma after being shot and beaten.

Prosecutor Eric Maillaud said investigators were told of a possible feud between Mr al-Hilli and his brother over money, but the sibling had gone to a police station to deny the row.

"The brother spontaneously went to see the police in Britain first to find out how his brother was because through the British media he had heard about the death of his brother," Mr Maillaud said yesterday.

"He turned up again because he heard about the conflict, the dispute between himself and his brother and he said, 'no, I don't have a conflict with my brother'."

Police plan to look at aspects of Mr al-Hilli's life to try to find a motive for the murders and also speak with his brother, named in reports as Zaid Hilli.

"Up until now the police in Britain were guaranteeing the safety of the house but now it's a Franco-British inquiry that is starting and we can now enter the house of Mr al-Hilli," Mr Maillaud said.

"His life, his job - I heard that he was the owner of three companies - all of that is the sort of thing that we have to find out about in England."

The four-year-old girl has spoken to police and confirmed that two of the victims were her parents, but said she did not know the Swedish woman very well.

Mr Maillaud said the girl remained under the care of psychiatric teams and had spoken about what he described as the "terror" of what happened, but did not see anything because she was hiding.

"The witness statement of the four-year-old girl, she just talked about a fury, a terror. She explained that from the beginning of the murder she was already between her mother and that other woman and she rushed under her mother's legs, her mother's skirt," Mr Maillaud said.

"I imagine she'll go back to Britain in a short timescale. We have to be able to identify members of her family, we have to make sure that they are people that can be trusted. You can imagine that we cannot entrust that little girl to the first person that turns up."

Her sister is not yet well enough to be interviewed but it is hoped she will be able to provide vital details of the attackers. Witnesses have said they saw a green four-wheel-drive vehicle in the area at the time of the killings, and possibly a motorbike.

All the victims were shot at least three times and investigators have found 25 spent bullet cartridges at the scene on the outskirts of a forest near Lake Annecy.

Mr Maillaud said the family had visited France a number of times before and it was not the first time they had been to Le Solitaire du Lac campsite in Saint-Jorioz, which was where they were staying when they died.

One theory is that shots could have been fired during a bungled armed robbery, with Mr Mollier being a witness to the crime.But speculation about other possible motives, including a pre-planned attack by professional hitmen, remained rife.

Some media reports have suggested that Mr al-Hilli, an engineer who left Saddam Hussein's Iraq several years ago, was known to the security services and was put under surveillance by Metropolitan Police Special Branch during the second Gulf war.

A Scotland Yard spokesman said they could not comment. But it is understood there is no link between the deaths and any national security issues.

Surrey Police said it was assisting the French authorities as they carry out a "complex" investigation. "As part of this, the force is facilitating a visit by French investigators to conduct inquiries in the UK," a spokesman said.

"We are unable to confirm any details around the investigation and it is inappropriate to make any further comment at this time."