An inquiry into the findings of BBC documentary The Secret Policeman is to be reviewed by the Police Complaints Authority.
Nine officers quit after The Secret Policeman was shown
Two senior officers from Hampshire Constabulary will visit Greater Manchester Police on Thursday to see how it is conducting its investigation.
In the programme, undercover reporter Mark Daly joined GMP as a trainee officer to expose racism and corruption in the force.
He was originally arrested, but will not now face charges.
His findings led to nine officers handing in their resignation - six from GMP, two from North Wales and one from Cheshire.
GMP opened an internal investigation almost a month ago after receiving unseen footage from programme makers.
A Police Complaints Authority spokesperson says that a 28-day review is usually carried out in all major inquiries to make sure nothing has been missed.