MI5 is not in the dock even though MPs are preparing to investigate the service's operations prior to soldier Lee Rigby's murder, a former defence secretary said today.
Parliament's Intelligence and Security Committee (ISC) will also answer whether or not security agencies fell short in the case of the Woolwich murder, its chairman Sir Malcolm Rifkind said.
Sir Malcolm added that the effect of Government spending cuts on the security services will be analysed during the ISC's review and any further reduction in resources would be a cause for concern.
Asked if MI5 was in the dock, Sir Malcolm told BBC Radio 4's Today programme: "No, I don't think they're in the dock. I think that would be very unfair.
"Do remember one fundamental point: the fact we have not had anyone killed until these tragic events in Woolwich since the 7/7 bombings (in London) in 2005 is not because there hasn't been terrorist plots.
"Every year since 2005 there has been at least one, sometimes two or even more, terrorist plots which were disrupted and prevented from killing British citizens, partly because of the work of MI5 - in some cases very largely because of the work of MI5 - and other intelligence agencies."
Earlier Sir Malcolm was asked if Government spending cuts have had an effect on the work of the security services.
He said: "There's been a very huge increase in the resources for MI5 and other intelligence agencies since the 7/7 bombings. They did have a reduction over the last year. That was investigated by the Intelligence and Security Committee. The evidence we got from the agencies themselves, not just MI5, was that was not too serious a problem for them.
"We would be concerned if there were to be any further reduction in resources for the intelligence agencies. Whether this is relevant to the Woolwichincident, frankly I'm not going to comment on it at the moment. We will go where the evidence takes us and we will come to a judgment as to whether that is indeed part of the problem, if there was a problem or if it's not relevant to this particular matter."
Sir Malcolm said he is very confident the committee will get to the bottom of MI5's work related to the Woolwich incident.
He said this confidence stemmed from the fact that MI5 head Andrew Parker has offered him assurances that he wishes to fully cooperate with the investigation and the ISC has Parliament-approved powers to access all relevant files and internal papers from MI5.
Sir Malcolm said that after the ISC deliberations, Prime Minister David Cameron and Parliament would receive a report.
He said elements of the Parliament report may be redacted for public viewing on the grounds of national security.