Lady Symons admitted that she was briefed about a Customs investigation into Sandline International's role in the matter on March 10. She said she had not told the House about the investigation later the same day because she had been briefed not to do so.

The minister described this decision as "quite right" because it would have been "highly prejudicial and quite wrong to make the [inquiry] public at that stage.

"Doing so would have alerted those who were potentially under investigation and would have been unfair to them if the allegations were subsequently found to be groundless."

'Specious nonsense'

Answering an emergency question in the Lords, she said she had first become aware of allegations about Sandline's operations in Sierra Leone from a report in The Observer on March 8.

Lady Symons said she was briefed by the Foreign Office two days later and told the Lords afterwards that the newspaper report had not been entirely correct - it had failed to mention arms shipments or breaking UN sanctions.

Lady Symons said all her briefing material had been made available to Sir Thomas Legg's inquiry into Whitehall's handling of the affair.

She said: "If any of my remarks, today or at any other time, are found to be inaccurate, I will correct them."