Fifty people in three small boats were intercepted while attempting to cross the English Channel on Sunday.
The Home Office confirmed a fourth boat was returned to France, and French authorities prevented a fifth crossing by a further 17 people in a dinghy.
Border Force has detained more than 671 people trying to cross the Channel in small boats so far during 2021.
That is double the number who attempted the crossing during the same period in 2020.
A Home Office spokesperson said: "People should claim asylum in the first safe country they reach and not risk their lives making these dangerous crossings. We are continuing to pursue the criminals behind these illegal crossings.
"The government is also returning illegal migrants who have no right to stay in the UK to safe countries.
"In January, new rules were introduced which make asylum claims inadmissible where people have travelled through safe countries to get to the UK through illegal routes."