Two gendarmes from Paris arrived wearing civilian dress at London City airport near the capital's financial district but did not speak to the media, an AFP reporter said.

Separately a gendarme from Annecy in eastern France, where the killings took place, arrived in Britain earlier Friday, official sources said, while another from Annecy was due in Britain on Saturday.

British-Iraqi man Saad al-Hilli, his wife, his mother-in-law and a bystander were shot dead on Wednesday.

The Hillis' two daughters survived. The youngest, aged four, was interviewed by police on Friday while the eldest, aged seven, is still in hospital after being shot and beaten.

Police in Surrey, the British county southwest of London where the family lived, confirmed the identities of the victims on Friday and said they were continuing to work with French authorities.

"This is a complex and ongoing investigation being led by the French authorities and Surrey Police is providing any assistance possible," Surrey Police said in a statement.

"As part of this, the force is facilitating a visit by French investigators to conduct enquiries in the UK.

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

French police have said they are investigating if a family feud over money could have been the motive. The brother of the British man slain in the attack has denied any such dispute to British police.