Keogh and O’Connor in Star Chamber.

Sir Nigel Swinewald, who was present at the Washington meeting, told government lawyers that the disclosure of the memo "could have a serious impact upon the international relations" of the UK, and was likely to have damaged the "promotion or protection" of British interests, including those of Prime Minister and himself.

Sir Nigel Sheinwald signed a certificate necessary to persuade the judge that the trial should be held in secret before Keogh and O'Connor were charged at the end of last year.