Four boats travelling across the Channel carrying 49 people have been intercepted by British authorities, with a further 22 people rescued by French authorities.
Border Force was alerted to the small vessels heading towards the UK coast at around 1.30am, the Home Office said.
Two cutters and a coastal patrol vessel were deployed to intercept the craft and rescue the group made up of men, women and one child.
The group presented themselves as Iranian, Iraqi and Afghan and will be medically assessed and transferred to immigration officials for interview.
The Home Office said further migrant activity was intercepted by the French authorities, with two other small boats taken back to France.
French sea rescuers received an alert in the early morning hours of a boat transporting 14 migrants who needed rescuing.
They were found in a state of hyperthermia and brought to a hospital in Boulogne-sur-Mer in northern France, joining eight others admitted a short while earlier, regional officials said.
The eight had taken to sea, trying to make their way to Britain, but turned back when their boat was spotted by patrollers.
In a statement the British Home Office said: "Illegal migration is a criminal activity.
"Those who seek to come to the UK illegally and the ruthless criminals who facilitate journeys are all breaking the law and endangering lives.
"When people arrive on our shores unlawfully, we will work to return them to mainland Europe.
"In partnership with France, we target the criminals behind this form of people smuggling, to pre-empt crossings and stop boats from leaving French shores."
The Home Office said patrols on French beaches had doubled and drones, specialist vehicles and detection equipment have been deployed to deter crossings.
Since January, more than 120 migrants who entered the UK illegally on small boats have been returned to Europe, the Home Office said.
National Crime Agency, Immigration Enforcement and Border Force officials are working with French police to prosecute people trafficking gangs.
In the last year, 16 French prosecutions saw 30 individuals convicted, receiving sentences ranging from three months to six years.
Commenting on the crossings, Natalie Elphicke, MP for Dover in Kent, said: "The people traffickers operate their illegal trade everyday of the year, including over the entire festive period from Christmas Day to New Year.
"The UK and the French authorities should be equally ready.
"In particular the French should be take firm action to stop these small craft setting off from the French coast.
"The weather was very mild on Christmas Day.
"These were perfect conditions for illegal departures from France.
"The French ought to have been more vigilant."
"Border force, the RNLI and HM Coastguard work tirelessly to save lives.
"But the truth is there should be an agreement between Britain and France that people who are found in the English Channel should be safely returned to France and not brought into Britain.
"That would be the best deterrent and the most effective way to bring this crisis to an end."
