A Scotland Yard officer, identified by the code name Laurence, told an inquest that he added the word "not" to his surveillance log, changing its meaning.

He said he had made an simple error, and there was "definitely" no cover-up.

Mr Menezes was shot dead in Stockwell in July 2005 by police who mistook him for suicide bomber Hussain Osman.

Surveillance officers completed the log on the evening after Mr de Menezes was shot at Stockwell Tube station in south London, the hearing into his death was told.

It was me that altered it, there's no doubt - it was my handwriting
'Laurence'

Part of it, in Laurence's handwriting, read: "A split second view of his face. And I believed it was not NT."

NT is the acronym for Nettletip, the code name for failed July 21 suicide bomber Hussain Osman.

Scientific analysis showed that the words "and" and "not" were added after the rest of the entry, the inquest heard.

'Nothing sinister'

Laurence was one of the specialist surveillance officers who followed Mr de Menezes as he travelled from his home in Tulse Hill, south London, to Stockwell Tube on July 22 2005.

He spoke on Thursday of his "disbelief" at being accused of conspiring to pervert the course of justice by changing the log entry.

The policeman said he must have spotted the error when reading through the log and amended it.

Jonathan Hough, counsel to the inquest, asked him: "You accept that you made a mistake but you say, is this right, there is nothing sinister to it, you haven't been trying to cover up anything?"

Laurence replied: "No, I have made a mistake unfortunately, but there is definitely no cover-up."

He added: "It was me that altered it, there's no doubt - it was my handwriting."

Phone and paper

Laurence had been given "words of advice" over the incident, but his senior officers had accepted he had not changed the log with "wrong intent", the inquest heard.

Earlier, the inquest heard that Mr de Menezes had not been seen to be carrying anything except a mobile phone and a paper before he was shot dead by police.

But the surveillance officer closest to him, codenamed Ivor, said he could not rule out him being a suicide bomber.

The inquest heard Ivor was the closest officer behind the 27-year-old electrician as he boarded a train at the station in south London.

Open jacket

Michael Mansfield QC, counsel for the de Menezes family, asked him: "From what you saw, there was nothing up to that point to suggest that he was a suicide bomber about to detonate a bomb, was there?"

Ivor replied: "I couldn't rule it out, sir, given what I saw, but effectively all I saw him carrying openly was a mobile phone and a newspaper on the train."

The surveillance officer said Mr de Menezes was wearing appropriate clothes for the weather that day, noting: "He was dressed virtually identical to myself."

Mr Mansfield told the inquest Mr de Menezes had his denim jacket undone "at all times" and was not carrying a bag.

He said a suicide bomber wearing a device on his body would generally detonate it by reaching into a pocket to connect wires to a battery.

Ivor told the inquest he could not remember seeing Mr de Menezes putting his hands in his pockets while he was following him.

But he said the police could not rule out the possibility that terrorists had different devices to those used in the July 7 2005 atrocities and the failed attacks on London a fortnight later.

The inquest continues.