The Home Ministry of India (doubt very much whether such things would have reached the level of the HM). The person who got that permission is now the Special Commissioner of Police - Vimla Mehra
"This concerns the request of Leslee Udwin for entering the Tihar jail to interview some convicts intimated by your letter dated July 22.
The ministry has no objection to the proposal provided informed written consent is obtained from each of the convicts interviewed," said a letter written by Home Ministry Joint Secretary S Suresh Kumar to Tihar director general Vimla Mehra on July 24, 2013
The file was disposed of at the level of the Joint Secretary with intimation to the then home secretary Anil Goswami, given the 'general nature' of the file, it never reached the then Home Minister Sushil Kumar Shinde