Cameras on the platform and the train were not operational, officers told the Independent Police Complaints Commission (IPCC). The submission by the Metropolitan Police, obtained by ITV News, puts officers at odds with a statement from Tube Lines, the company operating the station.

The police document says: "Stockwell station and environs has been surveyed and all existing CCTV has been seized.

"During the course of this it has been established that although there was onboard CCTV in the train, due to previous incidents the harddrive has been removed and not replaced.

"It has also been established that there has been a technical problem with the CCTV equipment on the relevant platform and no footage exists."

However in a statement to The Mail on Sunday, Tube Lines said: "We are not aware of any faults on CCTV cameras at that station on that day. Nothing of that nature has been reported to us." Yesterday the company refused to elaborate.

While some sources denied police had deliberately wiped the tapes, others remained convinced there was a cover-up.

One union official argued however that the on-board cameras may have been empty.

Employees' representatives said Met officers emptied the cameras the day before police killed Mr de Menezes as part of their investigation into the failed bombings on 21 July.

According to a report he would have passed eight cameras, two in the station entrance pointing at the barriers, another aimed at the Northern Line escalator and another on the way down.

When Mr de Menezes reached the bottom of the escalator, another camera would have captured him. And as he turned on to the platform one above the track and three more at each end of the platform would have caught him on film, the reports say.

This information should have been sent to a control room and passed to video tape. Yet there is apparently no footage of him in and around the platform.

The source, who is close to the investigation, said reports of a cover-up were "absolute rubbish''. The source said reports that the tapes had been handed back to London Underground staff were "nonsense'' because such material would have been kept as evidence in the ongoing inquiry.

A spokesman for the IPCC said: "We are not willing to comment about every story that comes up.''

But confusion still surrounds the contents of surveillance tapes taken from Stockwell station. Sources have suggested that the tapes had been recovered from the station booking hall, which had shown images of Mr de Menezes and that there was limited footage from cameras inside the carriage where the shooting took place.

All Northern Line Tube trains are equipped with CCTV - at either end of the carriages, but the only photograph published of the incident seems to have been taken from a doorway.

The confusion deepened as two senior Brazilian officials flew into London to examine the background to Mr de Menezes' death. The officials will want to know if CCTV footage of the incident exists. The Brazilian government has expressed "shock and bewilderment" over the death and has said it wants answers to "a number of matters".

Wagner Goncalves, of the federal prosecutor's office, and Marcio Pereira Pinto Garcia, of the ministry of justice, went from Heathrow airport to Scotland Yard, where they met senior officers led by deputy assistant commissioner John Yates. They are also due to meet members of the IPCC tomorrow.

Sir Ian Blair, the Metropolitan Police Commissioner, has faced unrelenting pressure since it emerged last week that initial police accounts of the killing were at variance with the facts.

Members of the Metropolitan Police Authority yesterday said Sir Ian still had their full confidence, but admitted that a public inquiry into the death appeared inevitable.

For the second time in two days, Downing Street issued a statement declaring the Prime Minister's complete confidence in the Commissioner.

A spokeswoman said Mr Blair, who is on holiday in Barbados, had been kept fully up to speed with the matter. She added: "The Prime Minister recognises that the Metropolitan Police, led by Sir Ian Blair, do a very difficult job and they do it very well."

Clare Short, the former Cabinet Minister, said it was now clear that the public had been misled over the death of Mr de Menezes. She told ITV News: " We've been lied to. This should be bigger than just calling for Sir Ian Blair to go. We need to find out exactly what happened. Who was telling the lies?"

As relatives and supporters of Mr de Menezes began a vigil outside Downing Street, his mother, Maria de Menezes, demanded justice for her son.

She said of the officers who shot: "They took my son's life. I am suffering because of that."

Speaking from Brazil, she told the BBC: "I want the policeman who did that punished. They ended not only my son's life but mine as well."

Mr de Menezes' cousin, Alessandro Pereira, handed a letter to Downing Street demanding a public inquiry.

The unanswered questions

* If the CCTV cameras showed Mr de Menezes using his Oyster card to open the ticket barrier, why did police sources suggest he vaulted it?

* Were cameras trained on the platform in full working order? Police and Tube sources contradict each other.

* How could all four cameras around the platform have failed at the same time?

* If the cameras had failed, why did the station log book contain no details of the fault?

* Why had CCTV onboard the train been removed?