The programme alleges one officer wore a Ku Klux Klan mask

Simon Ford was responding to criticisms by Home Secretary David Blunkett about the way a reporter posed as a probationary officer with Greater Manchester Police (GMP) to get the evidence.

The allegations, which will be broadcast on BBC One on Tuesday, have led to four officers being suspended, three from GMP and one from North Wales Police.

Footage for the programme includes one officer dressing up in an improvised Ku Klux Klan hood.

Reporter Mark Daly faces criminal charges over his move to infiltrate recruits as part of the work to assess whether institutional racism still exists within police ranks.

GMP has confirmed it suspended three officers after senior officers viewed footage from The Secret Policeman programme.

'Actual evidence'

On Tuesday Mr Ford, executive producer of the programme, defended the methods used to put together the evidence, which was recorded at Bruche National Training Centre in Warrington, Cheshire.

MARK DALY My life as secret policeman Black officers back reporter

"It is the first time ever of actual evidence of police racism," he told BBC Radio 4's Today programme.

"With investigative journalism we have produced evidence."

He said there have been "countless" reports into institutional racism in the police and a "huge number" of initiatives to deal with it, but the documentary shows racism has been "driven underground" at GMP.

Mr Daly claims to have recorded racist comments made, including one officer saying he would kill an Asian officer "if I could get away with it".

Another officer is heard to say: "I'll stop him cos he's a Paki. Sad innit but I would."

Ray Powell, president of the National Black Police Association said he was "disappointed" by the behaviour of a "handful" of recruits, who are featured in the programme.

"I hope this is not a reflection of what is taking place in our police training centres throughout the country," he said.

"I will be looking to senior figures in the police service to publicly condemn such racist behaviour and take immediate steps to root out other perpetrators."

'Covert stunt'

However, Mr Blunkett has questioned the BBC's "intent to create, not report" the story.

He has also suggested the BBC carried out a "covert stunt" and had leaked information to the media in an attempt to get publicity for the documentary.

Mr Daly spent five-and-a-half months with GMP and could face charges of obtaining a pecuniary advantage by deception and damaging police property.

He is due to answer bail in November.

The BBC has said any pay Mr Daly received has been kept in a separate bank account and was to be returned to the force at the end of the investigation.

Viewers in England, Wales and Northern Ireland can watch The Secret Policeman on BBC One at 2100 BST. It will be shown at 2235 BST on BBC One Scotland.