Under the new treaty, published on 4 August, external, France agreed to take back adults or accompanied children who make a journey to the UK by small boat, once any asylum claim is withdrawn or declared inadmissible.
Both countries have agreed to work towards making transfers with three months after small boat arrivals have entered the UK.
Former home secretary Yvette Cooper stressed the scheme starting up was a trial.
Details of how people will apply to come to the UK from France under the treaty have also been published by the government.
Successful applicants will initially be granted the right to come to the UK for three months, to “consider how to regularise their stay”.
Applicants will apply online – but have to submit proof to the Home Office they are applying from within France.
The UK has agreed to pay the transportation costs both of those migrants it sends to France, and those it accepts back in return.