Extraordinary allegations that Special Branch officers deliberately falsified vital evidence to hide mistakes which led to the killing of Jean Charles de Menezes at a south London Underground station were made last night.

According to claims in the News of the World, police altered the contents of a logbook, which detailed the Brazilian electrician's final movements, in a bid to cover up their blunders.

The 27-year-old was shot dead at Stockwell Tube station, in the wake of the London bombings, by police exercising a shoot-to-kill policy.

Specific words were understood to have been changed to cover up the fact that surveillance officers had wrongly identified Mr de Menezes as terror suspect Hussein Osman.

Alterations were hastily made to amend the wording of the official log once the shocking truth emerged that the dead man was not, in fact, the extremist wanted in connection with the failed 21 July Tube bombings.

This was in a bid to pass the blame for the shooting on to the firearms officers who actually shot the electrician and on to senior officers at Scotland Yard who were in charge of the operation.

These revelations are reportedly contained in the report of the Independent Police Complaints Commission (IPCC). Last night, despite calls to the Metropolitan Police, the Home Office and the IPCC, The Independent on Sunday was unable to corroborate or substantiate the claims.

The family of the dead man said the revelations were "shocking" and demanded an immediate public inquiry. Asad Rehman, the family's spokesman, said these latest reports reinforced their belief that there had been a deliberate cover-up over Mr de Menezes death.

"It reinforces their belief that his killing was not the result of a catalogue of errors but that there was something more malign behind this," said Mr Rehman, who has written to the Attorney General and the Crown Prosecution Service demanding an official inquiry into Mr de Menezes' death. "Yet again, the family has to find out through leaks what might have happened to Jean Charles. We believe a public inquiry is the only solution for the real truth to be established."

The story, if proved correct, will add to the controversy surrounding the shooting. Sir Ian Blair, the Commissioner of the Metropolitan Police, is already facing a separate inquiry into complaints made by Mr de Menezes' family that he made misleading comments about the shooting to the public.

The Stockwell killing has also highlighted communications failures between surveillance teams and commanding officers as well as calling into question Operation Kratos, the Met's secret policy on dealing with potential suicide bombers.

The IPCC review of the Stockwell killing was handed to lawyers at the CPS just over a week ago. Copies have also been delivered to Charles Clarke, the Home Secretary, as well as to the Metropolitan Police Authority and to Scotland Yard. It is expected that they could take up to a year to decide if there are sufficient grounds on which to bring a prosecution against any of the officers.

However, sources quoted by the News of the World allege that the IPCC report reveals that the log was altered from "it was Osman" to read instead "and it was not Osman".

The alteration should have been signed but was not. This was regarded as a clumsy error by the IPCC investigators. Their report says: "This looks like an attempt to try to distance Special Branch from the decision [to shoot de Menezes].