Police search teams with sniffer dogs and divers were scouring a stretch of the river a near Ealing Hospital when they found the blade.

The prime suspect in the case is Latvian builder Arnis Zalkalns , who disappeared a week after Alice from Hanwell went missing.

Police believe Mr Zalkans, who was jailed in his home country for the murder of his wife , may have fled back to Latvia .

However, detectives said it was too early to say if the knife was linked with the investigation into the disappearance of the 14-year-old, who has not been seen since August 28.

The hunt for missing Alice Gross is biggest police search since 7/7 bombings.

Detectives looking for the teenager and Arnis Zalkalns said they have used around 600 officers from eight forces in the hunt for vital clues to their whereabouts.

A total of 25sq km of open land has been looked over, along with 5.5km of canals and rivers.

The investigation has taken more than 630 calls as frantic members of the public scramble to help officers trace the 14-year-old.