On Thursday, a small number of failed asylum seekers, who landed on UK shores in October, were sent back to France.
The Home Office said it wanted to provide "a strong deterrent against the dangerous crossings".
The move is part of a new plan agreed by France and the UK which will see the UK spend an extra £3m on security.
It is understood fewer than five were returned to France on Thursday morning. The Home Office said it could not say where the migrants were from, nor whether they had travelled to the UK together in a small boat.
The measures come after a small spike in the number of migrants crossing the English Channel towards the end of last year.
Following talks with French ministers, Home Secretary Sajid Javid said: "Today's joint action plan strengthens our already strong relationship and increases joint action around keeping both our borders secure and discouraging these dangerous journeys."
Previously, the UK announced an extra £44.5m would be spent on strengthening Channel border security.
The home secretary has agreed now to spend £6m (of which £3m is new) on CCTV, night goggles and number plate recognition capability.
Extra security cameras will be placed at French ports and areas where migrants embark from, with a live feed viewable in the UK-France Coordination and Information Centre, in Calais, which is staffed by British and French agencies.
The Home Office said there would also be increased surveillance of the Channel by air and boat patrols, and more foot patrols on beaches and coastal areas.
Last week, UK Prime Minister Theresa May and French President Emmanuel Macron signed the Sandhurst Treaty which committed them to reducing the time taken to process migrants.
It means it would take one month, rather than six, to process a migrant hoping to come to the UK from Calais - and 25 days to process children.
Over the whole of last year, 539 people attempted to travel to the UK on small boats - 434 (around 80%) made their attempts in the last three months of the year, according to the Home Office.