The head of the Serious Fraud Office (SFO) has defended his decision to drop a corruption probe into a defence deal between BAE Systems and Saudi Arabia.
Speaking exclusively to the BBC, Robert Wardle said he had come under no political pressure to drop the inquiry.
Mr Wardle said he had made the decision independently, following warnings that continuing the probe could damage UK national security.
The SFO's decision in December sparked anger among opposition politicians.
SFO investigators had been probing claims that BAE paid bribes to secure a major arms deal in the 1980s.
The UK defence company denied all claims of corruption.
There were media claims in December that the Saudis had threatened to cancel a plan to buy 72 Eurofighter from BAE Systems unless the probe was halted.
The Eurofighter deal, which was negotiated between the Ministry of Defence and the Saudi government, is worth an estimated £10bn to BAE.
Mr Wardle said he had taken advice from the "highest levels", including the Attorney General, the Solicitor General and the British Ambassador to Saudi Arabia, before dropping the investigation into allegations surrounding the Al Yamamah arms deal.
"I made the decision, I made it independently, I made it on the basis of the information I had," he told the BBC's Newsnight.
"The difficulty was the public interest. To continue the investigation was going to cause damage, it was going to cause serious harm with our relations with Saudi Arabia," Mr Wardle said.
"That harm would have been reflected in a lack of co-operation, so I was told, that would seriously damage national security and international security."
Mr Wardle said dropping the probe was not "something we were entirely comfortable with", but he added: "Sometimes you have to make these sorts of decisions."
Mr Wardle admitted that SFO staff working on the investigation were "disappointed", but he insisted their morale remained high.
Attorney General Lord Goldsmith justified the SFO's decision in December, saying he believed a prosecution "could not be brought".
The move was criticised by opposition parties and by the Organisation for Economic Co-operation and Development, which said it sent the wrong message about tackling bribery and corruption.
In February, the Liberal Democrats asked the European Commission to look into the SFO's decision to determine whether the move breached competition regulations.
The SFO is looking at separate claims regarding BAE in South Africa, Tanzania, Romania, Chile, the Czech Republic and Qatar.