Birmingham criminals had to be held in a magistrates' court in London as there were no cells available locally.
The six men had just been sentenced at courts in the city but were taken 115 miles to Hammersmith on 11 June.
The Shadow Justice Minister, Edward Garnier, said it was a disgrace and the system was "breaking down".
The Ministry of Justice, the government department responsible for prisons, said it actively manages the prison population to ensure public protection.
Mr Garnier said: "You are sent 150 miles down the road to west London.
"(They went) not to a prison, but to a court, where there is no health check, there is no health staff, there is no mental health staff, there is no drugs staff (and) there are no sanitation facilities.
"But you are simply housed under the court. It seems to me the system is breaking down."