The UK is not sufficiently co-ordinating with France in efforts to reduce the number of migrants crossing the Channel in small boats, a French report said as part of a broader assessment pointing to the “uncertain effectiveness” of illegal migration policies.

France is “struggling to develop operational co-operation arrangements” with the UK, according to the report published on Thursday by France’s Court of Accounts, a body in charge of auditing the use of public funds, independent from the government and parliament.

The report refers in particular to a joint intelligence unit created in 2020 to fight human smuggling and reduce the number of people risking their lives to cross the Channel illegally.

In 2022, it helped dismantle seven illegal migration networks.

The court “found that the British don’t provide usable information on the departures of small boats, and give very general, first-level information that has not been counter-checked”.

Information on the circumstances in which migrants arrive and their nationalities and on boats “appears to be very patchy”, the report said.

“The relationship between France and the UK is therefore unbalanced in terms of information and intelligence exchange.”

The UK’s Ministry of Defence estimated that crossings of the English Channel by boat increased by at least 58% between 2021 and 2022, a year that saw more than 45,000 migrants arrive on British shores.

The report said 56% of crossing attempts were prevented that same year — unchanged from the year before.

The British Government announced this week that the number of migrants crossing fell by more than a third in 2023, to provisionally just over 29,000.

The UK’s Home Office said on Wednesday that another 26,000 “of these dangerous, illegal and unnecessary crossing attempts were prevented in 2023 thanks to our partnership with France”.

France in recent years has stepped up efforts to prevent migrants from crossing the Channel, including through more police, equipment and facilities.

The country received 222 million euros (£191.3 million) from the UK from 2018 to 2022 as part of a bilateral agreement and British Prime Minister Rishi Sunak last March promised £480 million for the 2023-2026 period.

The number of people living illegally in France is unknown, but researchers from the Pew Research Centre estimated their numbers in 2017 to be between 300,000 and 400,000, in a country of 67 million inhabitants.

This is about three times fewer migrants with no legal status than in the UK and Germany.

The Court of Account’s report assessed a series of other issues related to illegal immigration policies, which were subject to 133 changes in law in the past decade.

It pointed to the difficulty of implementing orders to leave the national territory, despite France carrying out the most deportations in the European Union.

More than 150,000 such decisions were made in 2022 and only 10% of the concerned people actually left, it said.

Amid recent debate over an immigration bill that focused largely on how to speed up the deportation process, the report said “international comparisons suggest that a change of scale is not realistic” regarding such policies.

UK authorities sent back about 3,500 people to their home country and Germany sent back about 13,000 people in 2022, according to statistics gathered by the French interior ministry.

Reasons listed by the report include French authorities’ difficulty to prove the identity of the concerned migrants, reluctance from home countries to issue authorisation to let them in and refusal by commercial airlines and plane pilots to take them onboard.

The Court of Account instead suggested enacting policies that would encourage migrants to voluntarily move back to their home countries by offering them money.

Such policies have been proven to have “significant efficiency”, the Court said, noting that France is lagging behind the UK and Germany in that respect.

Pierre Moscovici, head of the Court of Account, said on Thursday the body also recommends a better organisation of border guards and police to make them more efficient, noting that more people are illegally crossing the border, mostly from Italy and Spain, in recent years.

Irregular immigration costs France about 1.8 billion euros (£1.55 billion) each year and involves 16,000 state employees, police and military, the Court said.