Four migrants have tried to cross the English Channel on a makeshift raft made from two windsurfing boards tied together, and using shovels as paddles.
They were spotted in difficulty by a DFDS ferry off Calais at about 06:25 local time, and returned to France after the coastguard was alerted.
Three further vessels carrying a total of 40 migrants did manage to reach UK waters, and were brought to Dover.
At least 1,480 migrants have crossed to the UK during the coronavirus lockdown.
The Home Office said in the first incident on Wednesday, a group of 11 men and four women, who presented themselves as Iranian and Iraqi nationals, were intercepted by a Border Force vessel at about 02:58 BST.
Another vessel carrying 10 men and five women, who said they were Iranian, Afghani and Syrian nationals, was intercepted about 45 minutes later.
In the third incident, at about 05:00 BST, a vessel was discovered to be carrying 10 men who said they were from Iran, Yemen and Syria.
They were all brought to Dover and transferred to immigration officials for interview.
Where appropriate, they would be returned to France, the Home Office said.
The French authorities stopped about 35 individuals from making the crossing on Wednesday, it added.
Minister for Immigration Compliance and the Courts, Chris Philp, said France had stopped more than 500 migrants from crossing the Channel in the month of April.
"We are working closely with the French government to tackle these unacceptable crossings and bring the ruthless criminals who facilitate them to justice," he said.
In a record for a single day, 166 migrants arrived off the Kent coast in seven small boats on 3 June.
The total for 2020 so far is now more than 1,900.