Former Attorney-General Lord Goldsmith told Panorama the reporter's track record - he boasts of having secured more than 100 convictions in a 30-year career - had to be re-examined.
"The fact that somebody who has been accused by a judge of apparently not telling the truth may be instrumental in those convictions would certainly be a reason to ... examine them to see whether they are safe."
The programme repeatedly showed close-up images of Mahmood on his phone in a car and wearing his favourite disguise of an Arab keffiyeh headscarf and long robes.
He has spent his career hiding his identity and has been allowed to give evidence from behind a screen in court cases and at the Leveson inquiry into media abuses. He tried to use legal argument to prevent Panorama from showing his face.
The programme's presenter John Sweeney said: "We are identifying him tonight to make it more difficult for him to entrap people in the future."
In 2002 Goldsmith was asked by a judge to examine the collapsed prosecution in a supposed plot to kidnap Victoria Beckham and her children, after it emerged that Mahmood had paid thousands of pounds to one of the alleged conspirators, Florim Gashi.
After the trial collapsed, Gashi made allegations which led police to launch an investigation into Mahmood, but it was dropped because of "insufficient evidence".
Mahmood has hit back at the programme, saying Gashi is "thoroughly discredited as a witness". His lawyer, Justin Rushbrooke, dismissed the programme as a "hatchet job".
- Independent