Shadow Home Secretary David Davis has renewed his call for an independent inquiry into the 7 July London bombs.
Mr Davis has long called for an independent inquiry
He was responding to a Sunday Times article which claimed MI5 did not tell MPs about tapes of one of the bombers discussing how to make a bomb.
If true it was "scandalous" and showed the need for a new inquiry, Mr Davis told the BBC's Sunday AM programme.
He said "every other major security failure" under previous governments had been subject to public hearings.
Mr Davis told the AM programme that Mohammad Sidique Khan had also allegedly discussed saying goodbye to his family and his young child.
Earlier in the week the shadow home secretary raised concerns in the Commons over what was known when about the bombers, following the publication of two reports into the 7 July bombs.
A report by a committee of MPs found two of the four bombers, one of whom was Khan, had been known to security officers but the threat they posed had not been realised.
Following the publication of this report by the parliamentary Intelligence and Security Committee (ISC) and the government's separate account of the events, Home Secretary John Reid insisted there would be no public inquiry.
The ISC report said that a lack of resources had prevented security services from intercepting the 7 July bombers.
But Mr Davis said it appeared MPs had reached their conclusions on the attacks without having heard all the evidence.
"Every other major security failure under previous governments - whether it was the Falklands War or whether it was serious spy failures such as the penetration of MI6 and so on were all subject to major independent inquiries," he said.
The Home Office did not comment on the Sunday Times report.