The Iraq Inquiry led by Sir John Chilcot did not provide a “sufficient basis” for the Public Administration and Constitutional Affairs Committee (PACAC) to hold such a probe, the cross-party group of MPs said.
In a critical report on the Chilcot Inquiry, the MPs warned that it would still be possible for a Prime Minister to disregard the proper Cabinet decision-making process along the lines of Mr Blair’s notorious “I will be with you whatever” note to George Bush.
The PACAC also criticised the seven years that it took the Chilcot Inquiry to complete its work and said that for many people it had failed to “provide some closure”.
The committee did not explore whether the Commons was misled by Mr Blair but noted that Sir John had “absolved” Mr Blair from the accusation that he had made a “personal and demonstrable decision to deceive Parliament or the public”.
In its report, the PACAC said: “The question of whether Parliament was misled is constantly raised. We do not pass over this matter at all lightly, but after taking advice, we do not feel that Chilcot or any other inquiries provide a sufficient basis for PACAC to conduct such an inquiry.
“However, we think Parliament should be prepared to establish such an inquiry into the matter if any new and relevant material or facts emerge.”
The committee raised concerns that there were still insufficient safeguards to prevent Cabinet being sidelined by a prime minister, highlighting the example of the July 2002 note from Mr Blair to US president Mr Bush.
“It is generally agreed that the prime minister of the day should never have written ‘I will be with you whatever’ in his letter to the president of the United States, against the official advice and without the explicit agreement of his key ministers,” the report said.
“This is just one of a number of examples identified by the Iraq Inquiry of the breakdown of collective ministerial decision-making over the development of UK policy on Iraq before the invasion.
“It is no longer acceptable that the present arrangements should continue without stronger means to prevent key ministers, or even the whole Cabinet, from being side-lined.”
The report said the cabinet secretary - the head of the civil service - should be able to formally object to a decision if it has not been taken following the correct procedure.
Committee chairman Bernard Jenkin said: “At present, there is simply nothing even a cabinet secretary can do to stop a prime minister from doing this again at some time in the future, short of resignation.
“There was a lack of collective Cabinet decision-making, at a time when clear thinking and a culture of challenge was most needed. The failure to engage Cabinet on such decisions cannot be allowed to happen again, but there is no mechanism to ensure that.”
The committee said the length of the Chilcot Inquiry was “a matter for regret” and had “undermined both the very public confidence that the inquiry was established to strengthen, as well as the confidence in the inquiry itself”.
It suggested sweeping changes for future public inquiries, with a greater role for Parliament in establishing probes and setting their parameters.