Robert Wardle said "of course" he now questions whether he was right after two High Court judges officially quashed his decision earlier this month.

But he denied he was former Prime Minister Tony Blair's "fall guy" and insisted that at the time he believed he was "acting within the law".

The High Court had ruled that the SFO acted unlawfully by dropping its investigation into multi-billion pound arms deals between the company and Saudi Arabia during the 1980s.

However, they also gave the SFO the right to appeal to the House of Lords against the decision, which was reached after a case was brought by anti-arms campaigners.

Mr Wardle, who left the job earlier this month, said he made the decision independently after he "formed the view that I should stop the investigation in the public interest because of the risk to national and international security".

He said he was "surprised" at the High Court ruling.

Asked if he had any doubts he had done the right thing, he replied: "Of course I now have doubt because the administrative court says no I got it wrong.

"But subject to that, I think at the time I had no doubts that I was doing the right thing."

And asked if he felt he was used as a "patsy" by Tony Blair, he replied: "I didn't feel like a fall guy at the time. I certainly don't feel like one now.

"I was doing my job. I was making difficult decisions on cases, which is something I have been doing for the last five years, probably 20 years."

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