Media playback is unsupported on your device Media caption Footage from the BBC Panorama investigation

The record of undercover reporter Mazher Mahmood - the Fake Sheikh - needs to be re-examined, an ex-attorney general has told Panorama.

Lord Goldsmith said the fact the judge in the failed trial of Tulisa Contostavlos said he had lied was reason to look again.

A former News of the World colleague has told how they created elaborate stings to target celebrities unfairly.

Mr Mahmood told the BBC he used legitimate investigatory methods.

The reporter said he had helped secure about 100 convictions during his 30-year career at newspapers including the News of the World and Sunday Times.

Case collapsed

Some of Mr Mahmood's targets - including the former Grange Hill and London's Burning actor John Alford - were prosecuted and jailed based on his evidence.

But Mr Mahmood is currently suspended from the Sun on Sunday following the collapse of a drugs trial involving singer Tulisa Contostavlos.

The judge said there were strong grounds for believing Mr Mahmood had lied to the court to conceal the fact he had manipulated evidence.

Image caption Here is the image of Mazher Mahmood which he tried to stop the BBC from broadcasting

Former Attorney General Lord Goldsmith told Panorama Mr Mahmood's record needed 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 look at those convictions again and to examine them to see whether they are safe," he said.

Following the collapse of Ms Contostavlos's trial, the Crown Prosecution Service said it had identified three cases involving evidence from Mr Mahmood where there was no longer a realistic prospect of conviction.

It said no-one was currently in prison on the strength of the reporter's evidence, but it was also looking at past cases.

Drug dealers

Mr Mahmood's former associate Steve Grayson worked with Mr Mahmood on numerous stories in the 1990s.

One involved Page Three glamour model Emma Morgan, whom the pair led to believe she was being offered a lucrative contract for a Middle East bikini calendar.

But Mr Mahmood really wanted a story exposing her as a major drug pusher and had hired a man called Billy to assist.

Find out more Watch Panorama: The Fake Sheikh Exposed on BBC iPlayer. BBC iPlayer

"He is a drug dealer, we're drug dealers, we have paid this guy to supply the drugs to give to her," Grayson said.

Ms Morgan, who was 24 at the time, said she had been put under pressure for several hours to supply cocaine.

She had been asked to pick some up from Billy and give it to Mr Mahmood, which she had done.

Billy told Panorama: "The only real criminal was Mazher Mahmood, he gave me the money to buy the cocaine."

Ms Morgan said: "I was a fool, I was naive. To be foolish isn't a crime, to be naive isn't a crime, to do what he did is criminal.

"I haven't had the career I should have had. I haven't had the life I should have had. He's a horrible, horrible man."

Mr Mahmood denied acting improperly and said Panorama's account of events was wrong and misleading.

Solicitor Mark Lewis, who helped expose phone hacking at the News of the World and is representing some of Mr Mahmood's victims, told Panorama: "The damage that's caused, the damage for people's livelihoods, the amount of people have sent to prison, it's a far more serious thing than phone hacking ever was."

Mr Mahmood told Panorama he had spent his career investigating crime and wrongdoing, he had used legitimate investigatory methods and brought many individuals to justice. He said any criticism of him usually came from those he had exposed or people he had worked with who had an "axe to grind".

Watch Panorama: The Fake Sheikh Exposed on BBC watch again on iPlayer.