The Serious Fraud Office (SFO) has been cleared of unlawfully surrendering to pressure from Saudi Arabia when it dropped a corruption inquiry into a lucrative arms deal.

The then SFO Director Robert Wardle was praised by the Law Lords for taking a “courageous decision” in late 2006 in the face of Saudi threats to withdraw co-operation on anti-terrorism. The director resisted the pressure for as long as he could, said Baroness Hale.

“The great British public may still believe it was the risk to British commercial interests which caused him to give way, but the evidence is quite clear that this was not so,” Lady Hale said. “He only gave way when he was convinced that the threat of withdrawal of Saudi security co-operation was real and that the consequences would be an equally real risk to ‘British lives on British streets’.”

The SFO was investigating allegations that BAE, one of the world’s largest arms-makers, ran a £60 million “slush fund” offering sweeteners to officials from Saudi Arabia in return for lucrative contracts as part of the Al-Yamamah arms deal in the 1980s.

It took the case to the House of Lords after the High Court upheld a judicial review challenge brought by two campaign groups, Corner House Research and Campaign Against Arms Trade.

Two judges in the High Court ruled that the Saudi threat was a “successful attempt by a foreign government to pervert the course of justice in the United Kingdom”. Lord Justice Moses and Mr Justice Sullivan said the SFO and the Government made an “abject surrender” to “blatant threats”.