The UK Border Force has increased patrols along the south coast, after an "unprecedented" surge in migrants attempting to reach the UK.
Vessels have been redirected to the English Channel after 48 migrants - including a four-year-old boy - were rescued in five separate incidents over two days.
Officials are concerned that the number of Iranian migrants indicates criminal gangs have opened new smuggling networks from the country.
The first attempt to reach Britain began in the early hours of Tuesday when a stolen French fishing boat was stopped as it entered the Port of Dover with 17 suspected migrants - including three children - on board.
Lieutenant Ingrid Parrot, spokeswoman for the Maritime prefecture, the Border Force equivalent in France, said that the theft of the boat had been an “unprecedented operation” by migrants.
Speaking to the Telegraph, she suggested two reasons why attempted crossings - at 26 this year - were up from last year's total of 13. The most probable reason was the recent good weather, but "migrants are [also] seeking to cross before Brexit," she said.
Lt Parrot said criminal smuggling rings have become more organised in the last two years, culminating in the theft on Tuesday. Previously they had only attempted to cross the Channel in rickety makeshift vessels, even canoes, she said.
French authorities have had to change tactics in the past 12 months, Lt Parrot said, with a far more "joined-up approach" between maritime authorities, border forces and intelligence agencies. She said there was close cooperation between French and British authorities and work was ongoing to identify international smuggling rings.
On Tuesday afternoon, seven suspected migrants were also found in a lorry arriving from France at Dover docks. One person needed medical treatment on arrival.
Then on Wednesday, in the space of just over 12 hours, three groups of migrants risked their lives crossing some of the busiest shipping lanes in the world in small open boats in a desperate bid to reach Britain. Marine experts say if the attempts continue there "will be deaths".
At 4.30am nine Iranian migrants - including a woman and a four old boy - were rescued from a Rigid Hulled Inflatable Boat (RHIB) after the Coastguard and RNLI were scrambled to help a vessel reportedly in distress in the south west shipping lane. They escorted the RHIB to Dover's Western Docks where they were met by Border Force and immigration officials.
Border Force was next alerted at 9.15am by the Coastguard and RNLI to a small fishing vessel which had rescued 10 Iranian men off the Kent Coast. The tiny white boat, only designed to carry four people, was escorted into Dover by a lifeboat where it was met by Border Force officers.
Finally, at 2pm the crew of a Gas Tanker ship spotted a RHIB in a shipping lane off Ramsgate, Kent. Five people were picked up and taken on board the vessel, which then headed to Falmouth to hand the individuals over to Border Force officials.
One highly experienced sailor, who did not want to be named, said: "If this does not stop now there will be deaths, the Lifeboat crews will be picking up bodies out of the water rather than cold people on dinghies".
Dover and Deal MP Charlie Elphicke said: "To see so many brazen attempts to break into Britain in one week is unprecedented and deeply concerning.
"That people are taking the risk of crossing such a busy shipping route on small craft - some even with young children on board - shows just how desperate they are.
"The Home Office must act urgently to tackle this growing problem by boosting our borders budget and the number of skilled officers."
A Home Office spokesman said: "We are alert to the risk posed by people attempting to reach the UK illegally via small boats.
"This year we have increased the number of coastal patrol vessels and, in light of recent events, have stepped up deployments along the South-East coast."