The number of irregular migrants living in the UK and other large European countries has not changed for years despite hostile political discourse about migrants overwhelming the continent, according to researchers.

Migration researchers from 18 of the world’s leading universities and research organisations including the University of Oxford have released the public database as part of the MIrreM project, which measures irregular migration.

They said it is impossible to produce completely accurate data due to some people living below the radar for fear of immigration enforcement, but the methodology used is likely to produce more accurate estimates than previous research has done.

The researchers found there were between 2.6 and 3.2 million irregular migrants living in 12 European countries, including the UK, between 2016 and 2023, representing less than 1% of the total population of these countries. Overall, the irregular migrant population across the European countries does not appear to have definitively changed since 2008.

The estimated number of irregular migrants in the UK including asylum seekers, trafficking victims and undocumented migrants, is between 594,000 and 745,000 according to the report.

The database significantly updates previous assessments of the irregular migrant population in Europe, such as the estimates by the Clandestino research project dating back to 2008 and a study by Pew Research Centre in 2019 and offers new information at a time when there have been fundamental changes in the European migration landscape.

Irregular migration has been a key issue in successive elections in the UK and other European countries in recent years with politicians pledging to clamp down on immigration. This tends to be in response to a belief among many voters that too many migrants are arriving via clandestine means such as dinghies or concealing themselves in the backs of lorries. The new data challenges those perceptions.

In 2008, Clandestino estimated the irregular migrant population of 12 European countries at 1.8m to 3.8m. The MIrreM project increases the low estimate by 780,000 and decreases the high estimate by 460,000, creating a clearer picture of the total irregular migrant population in the countries studied.

The United States, which the new research used as a comparator, has the largest estimated irregular migrant population in terms of absolute numbers.

Finland has the smallest estimated irregular migrant population in terms of its size.

Compared with 2008 estimates, research from MIrreM indicates that in three countries, the new estimates suggest greater numbers – Austria, Germany and Spain.

In five countries, the estimated irregular migrant population remained the same – Belgium, France, Italy, the United Kingdom and the United States.

In five countries, it declined – Finland, Greece, Ireland, the Netherlands and Poland.

Michele LeVoy, director of the Platform for International Cooperation on Undocumented Migrants, said the new data could help design policies for this often hard-to-reach group. “Estimating how many people are living in an irregular situation in Europe must be used to design inclusive policies that grant access to public services for this marginalised population, and that offer them pathways out of irregularity. Undocumented people are already part and parcel of our societies and it’s high time that Europe recognised this.”

Louise Calvey, director of the charity Asylum Matters, welcomed the report. “The ‘migration crisis’ has been manufactured by failed governments and political leaders,” she said.

“They’ve used this narrative to justify the most pernicious anti-migrant policies our country has ever seen, closing safe routes, closing the asylum system and leaving people stuck in an unending legal purgatory.

“This report should be foundational to the Labour government’s approach to asylum and migration; work globally to build a fair and safe system of migration, treat people with dignity and respect, stop punishing people for needing to be here.”

The report comes as Home Office figures showed a total of 973 migrants in 17 small boats crossed the Channel to the UK on Saturday – the same day four people died – making it the busiest day of the year so far.

The arrivals brings the total for the year to 26,612 compared with 25,330 by the same date last year and 33,611 in 2022, with 1,368 having made the journey on Friday and Saturday combined, according to Home Office figures.