The Labour MP had originally invited a Channel 4 News team to accompany him on the visit, but the Home Office refused permission.
Mr Vaz inspected the detention centre after this programme aired footage filmed secretly by detainees at Harmondsworth and another centre, Yarl’s Wood.
The reports raised concerns over the medical treatment available to detainees and their mental health.
Mr Vaz spoke to a number of people being detained at the facility during his visit.
He said: “A lot of people are concerned about medical conditions. A lot of people are concerned because they don’t know when they can go. A number of people were concerned because they want to go back but they can’t go back.”
He added: “We need a facility that deals with those that have got a dangerous criminal past, who if they are allowed into the community, may commit those offences again, and who have no right to be in this country.
“There are other cases which do not merit coming in here, and that means we need to change the legislation.”
A detainee has told Channel 4 News that fighting broke out at another immigration centre at the Verne, a former prison in Dorset, last night.
The Home Office said it was aware of an incident at the facility. A spokesman said no detainees or staff were injured but the emergency services were called as a precaution.