A prisoner told the investigator that he could give "five ton [£500] to bring a bar of weed if you just let me know, and then once we both know it's right, we'll go to the 15-ton mark".
Another inmate spoke of witnessing inmates being paid in drugs to "assault a member of staff just to get that member of staff off the wing".
The prison which the undercover reporter worked is run by GSL - formally known as Group 4 - and was criticised before after the murder of one inmate along with the suicides of vulnerable inmates.
John Bates, director of corporate communications at GSL, was shown the footage and told the Guardian that mobile phone recoveries in the prison "would tend to suggest that there is a very prevalent problem".
He said the prison was progressing and that training was "extremely thorough".
The investigation claims that after the reporter underwent the 13-week training programme, he then found himself on some of the most dangerous wings while he was still a trainee, in addition to not having keys or a shortwave radio.
The Home Office said it was preparing a statement reacting to the claims.
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