New figures have revealed more than 3,500 migrants were detained in Kent after crossing the Channel at the height of last summer's crisis.
It comes as watchdogs criticised conditions at short-term immigration holding centres in the county, used to detain those who attempt to gain entry into the UK without being detected.
"Clandestine" migrants were hidden in vehicles on the ferry to Dover or in the Channel Tunnel, or on freight trains arriving in Folkestone, a report by HM Inspectorate of Prisons (HMIP) said.
Logs showed that there had been a 126% increase in detentions at the main holding facility at Dover Seaport last year. In the first nine months of 2014, there were 2,118 detentions, while in 2015, the figure had increased to 4,785.
In the three months to the end of September alone, there had been 2,781 detentions. In addition, 822 men were held at an overflow facility in Folkestone called Frontier House.
The combined total of 3,603 is equivalent to 1,200 people stopped a month - or 40 every day.
Throughout the summer migrants massed in Calais made thousands of attempts to reach Britain, with a number dying as they tried to make the journey. The crisis was said to have cost the economy millions of pounds as hauliers were forced to dispose of contaminated goods and wait in lengthy queues on the M20 in Kent.
Inspectors visited Dover Seaport, Frontier House and a third site in Folkestone - Longport freight shed.
The report said: "The Dover Seaport facility was "crowded, poorly ventilated and smelled badly. It was not designed to hold people for more than a few hours but over the summer detainees were held for an average of 18 hours. The holding room had religious books and a prayer mat, but no compass to indicate the direction of Mecca.
"There was nowhere suitable to rest, no shower facilities and no windows at Frontier House, while the pay phone did not work. Conditions at Longport freight shed were "wholly unacceptable", with detainees held overnight or for several hours with no clean or dry clothes, no food or hot drinks and nowhere to sleep other than on a concrete floor."
"There is no doubt that the increases in migration initially overwhelmed the existing facilities and an emergency response was required.
Inspectors did welcome plans to refurbish the holding room at Dover Seaport and said an area for detainees to receive support from third sector organisations was a "praiseworthy innovation".