GETTY Police in Sweden have performed wider people checks recently after an illegal migrant killed five

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In the past months, police have staged wider sweeps on workplaces to check papers, netting undocumented workers, sending a warning to employers and sparking heated debate in a nation that has been traditionally tolerant to migrants. In May, police carried out their biggest raid so far when dozens of officers swooped on a constructions site in Stockholm. Nine were caught and sent to detention centres, while another 40 escaped by scrambling onto scaffolding and across roof tops.

Swedish authorities had already started to tighten up on illegal immigrants, but police stepped up their activities after Uzbek construction worker Rakhmat Akilov drove into Stockholm shoppers in April. “We have an unlimited amount of work,” said Jerk Wiberg, who leads the Stockholm police unit in charge of domestic border controls. A 22-year veteran who has caught thousands of illegal immigrants, Wiberg led the raid at the construction site in May.

GETTY Police carried out their biggest raid in May on construction sites in Stockholm

After Akilov became another militant in Europe to use a truck as a weapon, Prime Minister Stefan Lofven made it clear that “no means no” for those whose asylum bids are rejected. Akilov, whose lawyer said he had admitted to committing the crime, had been in hiding after his asylum request was denied. The Migration Agency estimated 10,000 asylum-seekers a year will choose to disappear rather than be deported. Up to 50,000 undocumented immigrants already work in hotels, transport, construction and restaurants, the agency said last year. Migration Minister Morgan Johansson said that a “dual labour market ... where a growing group lives on the outside of society and remains in Sweden” after having been denied residency was unacceptable.

GETTY Uzbek construction worker Rakhmat Akilov drove into Stockholm shoppers in April killing five people

Stockholm terror attack in pictures Fri, April 7, 2017 The vehicle drove into crowds on Drottninggatan (Queen Street) - one of the city's major pedestrian streets, just before 3pm local time, before crashing into Åhlens Mall Play slideshow Twitter 1 of 33 Truck rams into crowds in central Stockholm

“It also increases the risk of them being exploited. We cannot have it that way,” he said, adding: “One way is to go after the employers ... (using) expanded workplace checks.” While cheap migrant labour is welcomed by some small businesses, government officials and economists worry that the shadow economy undercuts Sweden's economic model, whose generous welfare provisions and high wages are built on high rates of productivity and one of the world's heaviest tax regimes. Tough measures against immigrants go against the grain for many in Sweden, a country of 10 million which once called itself “a humanitarian superpower” that generously welcomed migrants fleeing conflict in the Middle East and Africa.

GETTY Stefan Lofven made it clear that “no means no” for whose asylum bids are rejected