The United Kingdom and France on Tuesday ratified and brought into force a “one-in, one-out” treaty that allows London to return some migrants who arrive across the English Channel in small boats, while accepting an equal number of vetted asylum seekers from France. British authorities said detentions of new small-boat arrivals will begin within days, with the first transfers expected to follow within weeks. Under the pilot scheme, which runs until June 2026, France will take back undocumented migrants deemed ineligible for asylum in Britain, and the UK will admit applicants with family ties or other links who have not attempted irregular crossings. The Home Office confirmed that the UK will pay all transport costs and has earmarked £100 million for additional National Crime Agency officers and technology aimed at disrupting smuggling networks. Home Secretary Yvette Cooper declined to give operational targets, saying numbers would "start lower and then build," but government sources have indicated around 50 returns a week—about 2,600 a year—are envisaged. More than 25,000 people have already crossed to Britain in small boats this year, heightening political pressure on Prime Minister Keir Starmer, whose Labour government faces criticism from both human-rights groups and anti-immigration opponents. French Interior Minister Bruno Retailleau said the accord’s goal is to dismantle people-smuggling operations, while the European Commission has approved the arrangement. Critics argue the scale is too limited to act as a deterrent, and campaigners warn the policy risks shifting the humanitarian burden back to northern France. Ministers in London insist the deal forms part of a broader border-security agenda that also targets online advertising of illegal routes and illicit employment.