Three more boats with suspected migrants on board have been picked up by the coastguard off the Kent coast.
Seven men, one woman and a toddler were on board a "small open boat", while 10 men were understood to be on another. They are all believed to be Iranian.
The coastguard was alerted to the first vessel "in distress in the south west shipping lane" at 04:30 GMT. The second boat was spotted at about 09:00 GMT.
Later, five people were rescued from a small boat several miles off Ramsgate.
There has been a spate of suspected migrants intercepted at or near Dover in the past week.
On Tuesday, a French fishing boat that was thought to have been stolen was stopped as it entered the Port of Dover with 17 suspected migrants on board.
In a separate incident, seven suspected migrants were also found in a lorry at Dover docks.
The latest boats were brought into Dover Harbour and the occupants have been handed over to Border Force officers.
Dover and Deal MP Charlie Elphicke urged the Home Office to tackle the growing problem of "these attempts to break into Britain", which were coming "thick and fast and becoming more shocking by the day".
"That people would take the risk of crossing the Channel on a small open boat with a toddler on board shows just how desperate they are," he said.
'Law abiding country'
In a statement the Home Office confirmed a coastal patrol vessel (CPV) had intercepted a rigid-hulled inflatable boat (RHIB) shortly before 05:00 GMT.
It also said the 10 men on the second boat, which had been spotted at about 09:15 off the Kent coast, had "presented themselves as Iranian nationals".
Meanwhile, five people, believed to be migrants, have been rescued from an RHIB several miles off Ramsgate at about 14:00, the Home Office said. They were picked up by a passing tanker, and will be passed over the Border Force when the boat docks in the UK, a spokesman said.
He said: "We are alert to the risk posed by people attempting to reach the UK illegally via small boats."
Middle East commentator Hazhir Teimourian told BBC Radio Kent that Iran was one of "the most repressive states in the world".
"On top of that, Iran's economy is a basket case," he said, adding that some Iranian migrants who make it as far as Europe saw Britain as a law-abiding country, and "being soft on people who claim asylum".