Then Leader of the Commons Robin Cook resigned over the matter and Mr Grogan suggested other members of the Cabinet at the time should have asked more questions.
Mr Grogan said: “On the night before the Iraq vote I recall Robin Cook clearly setting out in his resignation speech that Iraq had no weapons of mass destruction and that there were other options than going to war.
“The Cabinet at the time bears a heavy responsibility for not following his lead and questioning the rush to conflict.
“A basic examination of the history of Iraq and previous British involvement in the Middle East should have led to a more cautious approach.”
Former Keighley MP Ann Cryer admitted at the time she had endured sleepless nights over opposing the Government but insisted she had always been confident of her decision.
She said: “I was completely convinced I was right and as things have unravelled over the months and years we don’t need any further proof.
“It was a tremendously hard time, I am not an automatic oppositionist. I thought carefully and long and hard about that decision.”
Mrs Cryer added: “I am just sorry I wasn’t, and my friends weren’t able to persuade the prime minister he was going down the wrong road.”