A police officer who was urinating in his surveillance van when Jean Charles de Menezes walked past yesterday denied failing to pay attention.

The officer, who was serving a temporary spell at Scotland Yard from the armed forces, insisted he had not neglected his duties by failing to film the Brazilian electrician.

He said he still managed to get a good look at Mr de Menezes leaving his flat in Tulse Hill, south London.

When asked how he failed to film the incident, he added: "I had one spare hand at the time and I grabbed the radio and transmitted."

After the operations room was told "he's worth another look", surveillance officers held back from stopping Mr de Menezes before he got on a bus over fears for the safety of mothers and children nearby, the inquest heard.

The officer, named as Frank, told the inquest how he initially believed Mr de Menezes was not failed suicide bomber Hussain Osman but then "changed" his mind.

When asked whether he felt he did the right thing by putting down his video camera when he was "caught short", Frank said: "Yes sir."

Mr de Menezes, 27, was shot seven times in the head at Stockwell Tube station on July 22, 2005.

He was tracked by surveillance after leaving the block of flats in Scotia Road, which were linked to Osman.

Michael Mansfield, QC, for the de Menezes family, said surveillance information Frank gave over the radio was "neither here nor there".

Mr Mansfield also said that the fact Mr de Menezes was not stopped from getting on the bus was possibly one of the greatest failures in the investigation.

Explaining how he managed to catch sight of Mr de Menezes, Frank said: "My initial thought was that it was a negative. It was only when Mr de Menezes walked closer to me that I actually compared him to the picture I had. I then said it was probably worth somebody else having a look."

When asked why Mr de Menezes was not stopped before he boarded a bus towards Stockwell, another surveillance officer, known as Edward, said there were fears over the safety of children and parents. He added: "I chose to remain in the vehicle, remain covert."

More than 30 photographs that could have stopped marksmen mistaking Mr de Menezes for a suicide bomber went unchecked by police, it also emerged.

Officers who shot dead the Brazilian electrician relied on a "poor-quality" CCTV image and a gym card picture.