A SOUTHAMPTON MP has called for a public inquiry into the 7/7 London terrorist attacks after it was revealed security services had tracked the perpetrators 16 months earlier but failed to arrest them.

The disclosures emerged as five British men with links to the 7/7 bombers were sentenced to life for a failed plot to set off a wave of fertiliser-based explosions around the country.

John Denham, Labour MP for Southampton Itchen, said an investigation into the role played by the police and intelligence services would be "valuable" to clear the air and help learn lessons for the future.

He cautioned that because of ongoing criminal investigations it might be difficult to be sure what the inquiry would be permitted to "discuss publicly".

And he stressed he would not want it to become a witch hunt against individual officers.

But he said: "I think a public inquiry would be valuable, to clear the air and learn the lessons for the future, not in terms of trying to hunt down someone who may have made an error of judgement under very difficult circumstances."

Mr Denham, who is the chairman of the Commons Home Affairs Select Committee, accepted that the inquiry would divert resources from efforts to prevent future attacks.

But he said: "That has to be balanced against the bigger aim of trying to assure people any lessons that needed to be learnt have already been learnt and put into place."

He added that over the next 10, 20 or 30 years, encouraging people to support democracy would be more important to preventing terrorist attacks than the security services.

He said: "It's winning hearts and minds rather than the work of the intelligence services that is likely to keep us safe."

Home Secretary John Reid rejected Mr Denham's call for a public inquiry but said a committee of MPs would examine the lessons learned from the fertiliser bomb plot trial.

Mr Reid told the Commons yesterday's events would "bring back the hurt and anguish" of the families of the July 7 victims.

He said a public inquiry would "divert the energy and efforts" of the security services.

The bombs, on July 7 2005, killed 52 people on London's transport network.