The first episode saw all four sets of participants successfully evade detection using "well documented and publicised methods used by illegal entrants and refugees."
The series was initially pulled from the schedules after the lorry tragedy.
Producers of the show believe they have shown major weaknesses with border checks, and there is a public interest in showing UK audiences these flaws.
How does the show work?
The show used British people in various scenarios attempting to cross into the UK.
One man successfully re-entered the country from the Netherlands by using a friend's passport.
Sitting in the back seat of a car, passport officials did not discover he was not the passport holder - despite having access to high quality imagery to help them identify those using documents fraudulently.
Another managed to enter the United Kingdom by hiding in the back of a camper van.
Whilst border authorities asked if their vehicle was locked during the ferry crossing, they did not inspect it for clandestine passengers.
Those taking part travelled with a show producer and reportedly had access to the correct travel documents, if asked to present them.
What has the response to the show been?
They added: "Organised crime gangs have no respect for human life so it is reckless to provide a platform for the illegal activity that they facilitate.
"Doing so can encourage them to exploit our border for profit, risking the lives of vulnerable, desperate people as they do so."
Channel 4 has defended its decision to produce and broadcast the programme, which was filmed in the summer.
A spokesperson for the broadcaster said: "This documentary series investigates concerns that the UK Border Force is failing to adequately secure the UK from clandestine entrants."
They continued: "Filmed this summer, the programmes question the security of UK borders and give the viewing public a much broader insight into an important issue facing this country - which is part of our remit as a public service broadcaster.
"More than ever, following this awful tragedy, the shocking findings of the films have become a matter of urgent public interest."
Responding to accusations they are giving a platform for the work of smuggling gangs, a Channel 4 statement continued: "All of the methods of entry into the UK tested in the programme are well documented and publicised methods used by illegal entrants and refugees.
"The only surprise in the programme is just how easy it is to enter the UK undetected. The shocking findings of these films are a matter of urgent public interest."