The Immigration and Nationality Directorate, based at Lunar House in Croydon, deals with 180,000 applications each year and fast-tracked the visa for David Blunkett's lover's nanny.
But it is also notorious for being the civil service workplace with a very high number of staff suicides, and for the body-searching of clients.
Civic activism charity South London Citizens is to hold a 'citizen's inquiry' into the directorate, which will hear testimonies from both staff and users of the service.
Organiser Neil Jameson said: "We think we will uncover a whole series of horror stories from both staff and users about how this service operates in a civilised country."
But the charity has received a mixed response from refugee and asylum organisations that it has asked to contribute to the inquiry. "Some have said that (the inquiry) will destroy the carefully nurtured relationships they have built up over the years at Lunar House," said Jameson.
The inquiry will be led by the former Bishop of Southwark, Charles Henderson and human rights lawyer, Eleanor Sharpston. A hearing will take place on 5 March at Croydon Town Hall.
Henderson said: "I hope this inquiry will bring some sanity to the hysteria surrounding the directorate and its difficult work. I encourage all users and staff to attend."
South London Citizens is a sister charity of the East London Communities Organisation which has campaigned to force financial institutions in Canary Wharf to pay a 'living wage' to contract cleaners.
- South London Citizens to hold inquiry into Immigration and Nationality Directorate
- The directorate processes 180,000 applications a year
- Proceedings to be chaired by former Bishop of Southwark and a human rights lawyer
- Inquiry threatens to reveal "horror stories". Some charities reluctant to take part.