How will the deal work?

Britain will be able to send migrants back to France but must accept an equal number of asylum seekers who are in France. Migrants identified for deportation will be detained in immigration removal centres. Britain must inform France of its intention to return an individual within 14 days of them arriving and the person must be removed within three months.

Asylum seekers in France who wish to take advantage of the reciprocal deal can apply on an online portal but must fit criteria, including having a family connection in the UK.

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How many migrants will be returned to France?

The treaty does not say and Yvette Cooper, the home secretary, refused to disclose a figure due to fears it would aid people smugglers. However, it is understood that about 50 migrants per week will initially be exchanged, which would equate to 1 in every 17 arrivals.

French police officer confronts migrants in a small boat attempting to cross the English Channel.

So far this year 25,436 migrants have crossed the Channel

SAMEER AL-DOUMY/AFP/GETTY IMAGES

How long will the arrangement be in place?

The deal is due to expire on June 11 next year, and can be terminated by either side with a month’s notice or suspended with a week’s notice.

The UK government hopes to renew the scheme as it sees the deal as a key measure to deter migrants making crossings, which are at record levels. So far this year 25,436 have crossed, 49 per cent more than 17,031 who had arrived by this time last year.

Can migrants stop their return to France?

They can try, by lodging legal appeals, but ministers are confident that they have a robust litigation strategy.

The treaty says a migrant can only be returned to France if there are no outstanding human rights claims or any other “judicial remedies”, live injunctions or court orders lodged against their removal from the UK.

Can France refuse to take individuals?

Yes. The terms of the treaty state that France and EU member states will have an effective veto. France can reject the request if it “considers that an individual would be a threat to public policy, internal security, public health or the international relations of any of the Schengen states,” which refers to the 29 European countries that have removed controls between their borders. The treaty says France must give a response within 28 days for each migrant Britain intends to return. However, if France ignores the request, the migrant must remain in the UK.

Will it stop the boats?

It’s unlikely because it is only a pilot scheme. Given it is understood that the initial exchanges will equate to 1 in every 17 arrivals, this is unlikely to deter migrants giving it a go as they will fancy their chances of avoiding deportation.

How many migrants need to be sent back to stop the boats?

A senior Home Office source said modelling carried out by officials had estimated measures to combat crossings would need to prevent as many as 85 per cent of all attempts to destroy people smugglers’ business model. It is highly unlikely the deal will return anywhere near 85 per cent of migrants.