The British government is resistingcalls for a public inquiryafter news that its domestic spyservice was watching two of four suicide bombersmore than a year beforethey killed52 London subway and bus passengers in 2005.

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A woman lays flowers at the Edgware Road tube station in London after 52 London transit riders died when suicide bombers struck on July 7, 2005. ((James Vellacott/Associated Press))

The spy service, MI-5, took no action against Shehzad Tanweer and Mohammad Sidique Khan, who were tailedbecause of their association withpeople under investigation in a separate case.

Themissed chance came to lightina trial in which five men received life sentences on Monday for a foiledplot to build a huge fertilizer bomb.

The CBC's Harry Forestell, reporting from London, said one of the startling revelations of the fertilizer-plot case was that agents trailing the ringleader, Omar Khyam, saw him meeting with Tanweer and Khan 15 months before the transit bombings.

"It now appears that police failed to understand the significance of the new players, with tragic consequences on July 7, 2005," he said.

"Investigators say they had to pick and choose which spots they believed to be the greatest threats. Counterterrorism officials say they simply had too few people and too many potential plots to follow up on."

British officials nowbelieve that the four suicide bombers and five fertilizer-bomb plotters, alongwith Canadian suspect Momin Khawaja, were all part of the same organized cell, he said.

Khawaja, an Ottawa software developer,was named as a co-conspirator in thefertilizer bombtrial but not charged. Heis awaiting trial in Canada on separate charges.

ABritish parliamentary committee is preparing to take a closer look at why MI-5 agents failed to follow up on leads that might have tipped them off to plot.

But Home Secretary John Reid has ruled out a public inquiry despite calls for an airing ofcase by survivors of the transit bombings and relatives of victims, the BBC reported.

MI-5, formally called the Security Service,gets itspopular name from the fact that it was onceknown as Military Intelligence section 5. Its sister agency, MI-6,is Britain's foreign spy service.

Headlines aboutMI-5's missedopportunity prompted its director-general, Jonathan Evans, to issue an unusual public statement.

"The attack on 7 July in London was a terrible event," he said. "The sense of disappointment, felt across the service, at not being able to prevent the attack (despite our efforts to prevent all such atrocities) will always be with us."

But he added: "The reality is that whilst we will continue to do everything in our power to protect the U.K. public, we must be honest about what can and cannot be prevented in a democratic society that values its freedoms."