Panorama's twice-postponed programme investigating Sun reporter Mazher Mahmood is set to be broadcast at 8.30pm.
According to the BBC Fake Sheikh: Exposed accused Mahmood of using "sophisticated entrapment and fabricating evidence".
In August the drugs trial of singer Tulisa collapsed after the judge said Mahmood had given dishonest tetimony.
Mahmood tried and failed to get injunction banning the BBC from publishing recent images of him. He also warned that broadcasting the programme could prejudice possible criminal proceedings against him
The Attorney General has also warned the BBC against broadcasting the programme in case Mahmood is arrested.
Yesterday, Mahmood issued a statement condemning the BBC and saying the programme was based on testimony from sources who were not reliable: former Mahmood informant Florim Gashi and former News of the World photographer Steve Grayson.
Today Grayson told Press Gazette: "Regarding the statement that was put out yesterday by Mazher Mahmood: we were close colleagues for some years, working together on a daily basis, which is why Panorama asked for my contribution. The back story of the Bodmin Moor piece would make an interesting programme in itself, but that’s a story for another day, when the real truth might stand a chance. Responding to Mahmood’s comments in the meantime would serve no purpose.
"I actually feel quite sorry for the man. I understand he lives behind a metal-secured door and has a personal bodyguard. A man who turns over his own family is no man at all, in my opinion."
This is believed to be a reference to the fact that Mahmood got his start in journalism when, as an 18-year-old he exposed some family friends who were selling pirate videos.
Grayson said: "I’m sure one day he’ll call to thank me for exposing him for what he’s become and for nudging him back on to the straight and narrow, if that’s possible. Because the sad thing is, he was basically a very good journalist until he started to believe he really was a rich Arab. It became about getting a story at any cost."
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