Two pressure groups won permission to bring a High Court challenge over the decision to end investigations into alleged bribery and corruption involving BAE Systems and Saudi Arabia.
Corner House Research, a group that campaigns for enforcement of the law in overseas corruption offences, and the Campaign Against Arms Trade were both given permission to seek judicial review.
Lord Justice Moses, sitting with Mr Justice Irwin, said "matters of concern and public importance" had been raised and the challenge "cries out for a hearing".
At the full hearing, lawyers for the campaign groups will argue that in December last year, Robert Wardle, director of the Serious Fraud Office (SFO), "misdirected himself in law" when he announced the decision to discontinue the investigations relating to the Al Yamamah defence contract.
Critics said he had to make his decision after coming under "heavy pressure" from the then prime minister Tony Blair and the Saudi government.
Dinah Rose QC, for the campaign groups, is accusing the director of misdirecting himself in law by taking into account the "irrelevant consideration" that continuing the investigation would risk prejudicing Saudi Arabia's co-operation with the UK on counter-terrorism, which would have an adverse effect on national security.
The QC contends that Article 5 of the OECD anti-bribery convention precludes the UK from taking into acccount the potential effect of an investigation or prosecution on another state - even where there was concern over its impact on national security. The SFO argues there was no misdirection.
Ruling that Ms Rose had made out an arguable case and the campaign groups should have permission for a full hearing, Lord Justice Moses said: "What is primarily contended is that this decision was taken under a misapprehension as to the meaning and effect of Article 5.
"I make no comment as to the cogency or otherwise of the arguments of the claimants, and I don't want anyone to understand that, by the permission I am about to give, that I have formed any view about the strength of those arguments."
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The claimants "undoubtedly faced formidable difficulties" in bringing their challenge, but they had raised a matter of public importance closely concerning the courts and legal system - "something which judges are here to protect," said the judge.
