Mr Cook, facing the last of 11 public sessions between the Foreign Affairs Select Committee and Foreign Office ministers or officials on the issue, claimed the MPs' inquiry had simply covered old ground.
The official inquiry by Sir Thomas Legg, published in July, had provided a full version of what happened, Mr Cook suggested. The Foreign Office had already acted on its recommendations.
"I don't think your hearings have covered a single material fact that was not already in Legg," Mr Cook said.
He criticised the committee's attempt to investigate the matter while Sir Thomas' inquiry was going on, saying it would have placed a "double jeopardy" on officials.
Since it emerged in May that officials met mercenaries who shipped arms to Sierra Leone in breach of an embargo, Mr Cook has appeared before the committee three times. His junior minister, Tony Lloyd, has appeared twice. Sir John Kerr, the Foreign Office permanent secretary, has appeared five times. The High Commissioner to Sierra Leone, Peter Penfold, appeared once.
Yesterday the Foreign Secretary said he accepted mistakes had been made. A more politically aware atmosphere in the Foreign Office might have led to the issue being drawn to his attention sooner, he said. He also criticised Mr Penfold for not making sure he had a copy of the order which confirmed the embargo in British law.
Mr Cook said the FO was looking into a report that GCHQ had warned his department about Sandline International's plans to aid the exiled government of President Ahmed Tejan Kabbah, but had not been believed. He said as not aware of any such communication.
A Foreign Office spokesman said GCHQ officials "have confirmed there is no substance to these allegations".Reuse content