The Brazilian's relatives said they had been told that the two "senior officers" yet to be questioned by the Independent Police Complaints Commission were not available for interviews until late July or even August.

As a result, the "Stockwell 2" investigation - which is probing the handling of the case following the shooting in London last July - could be delayed until at least late summer.

The news comes as a pre-inquest review is held on Friday at Southwark Coroner's Court into the progress of the original investigation into the actual shooting itself.

The IPCC handed that report to the Crown Prosecution Service in January and the CPS is soon expected to announce if any charges will be brought against officers involved in the shooting.

Members of Mr de Menezes' family said they would be attending the private hearing to express their frustration at the delays in the CPS's announcement.

A date for a full inquest into the death cannot be fixed until any decision on criminal charges is made.

A spokesman said: "The family has already been let down by the police, now it is being let down by the CPS and IPCC.

"It is an outrage that neither agency have finished their investigations and the CPS have not indicated to the family the timescale.

"This adds further insult to injury to the family as they approach the one-year anniversary of Jean's murder."