More than 30 people have been arrested across the UK in a Home Office crackdown against people-smuggling gangs exploiting the invisible border between the Republic of Ireland and Northern Ireland and between Ireland and Wales.

The operation, which took place between 16 and 18 September, resulted in 14 arrests in Belfast and £400,000 in cash and 10 false ID documents seized at various locations across the UK.

The swoop comes months after concerns were raised in Ireland that people smugglers were transporting people in the other direction – from the UK to Ireland in response to the threat of being deported to Rwanda, a potential consequence of the then official British government policy which has now scrapped.

The Home Office said on Sunday that its enforcement teams and UK police forces descended on ports, airports and roads in locations including Belfast, Scotland, Liverpool and Luton as part of the three-day operation.

Of those arrested in Belfast, seven were Albanian nationals. A man from Iran who had been intercepted at Belfast airport with three allegedly falsified documents with his image was also detained. He had flown into Dublin airport the previous day.

Police also arrested a Jordanian, a Ukrainian, a Georgian, a Syrian, and Sudanese and a Chinese national. Seventeen people were arrested in Northern Ireland.

The Home Office said nine people were arrested in Holyhead, the main ferry port from Britain to Dublin, three in Liverpool port which runs ferries to Belfast, and one at Luton airport.

In all 20 of the 31 arrested were detained for attempted illegal entry into the UK from Ireland or Northern Ireland or in breach of deportation order, one was arrested for “assisting unlawful immigration” and nine were arrested on allegations they were trying to “enter or leave” Ireland “by deception” or “abuse” of the common travel area.

The enforcement inspector Jonathan Evans described the operation across ports and airports as a huge success that “sends a clear message that the smuggling gangs who break our laws will face serious consequences”.

He said his office, which Labour recently set up, was “taking action day in, day out” to ensure they were one step ahead of people smugglers. “We will continue working relentlessly to ensure no one abuses the common travel area or the UK’s borders,” he said.

Under an agreement that dates back to Irish independence in 1922, no government-mandated passport or other physical checks exist for British and Irish citizens travelling between their two countries. It is part of a longstanding agreement called the common travel area and does not apply to non-British or non-Irish nationals.

But the porous nature of the border has been the source of political flare-ups.

It was one of the main sticking points in Brexit with the Irish finally securing legal guarantees in the 2019 deal that the border would remain invisible without passport or customs checks.

In 2022, however, the then British home secretary, Priti Patel, told the Irish government she was concerned the invisible border would provide a backdoor for refugees arriving in Ireland to enter the UK without a visa.

Irish politicians said the suggestion was “disgraceful” and “terrible”. They had sought and secured further guarantees during Brexit negotiations that no checks would be conducted on cars, trains or trucks crossing the Northern Irish border.

Irish and British police forces have cooperated in the past on limiting opportunities for people smugglers using Dublin airport to get into the UK under a joint initiative, Operation Gull, but it continues to be a sensitive subject for both governments given the pitfalls of the invisible border.

An Irish minister claimed earlier this year that 80% of asylum seekers coming to the republic arrived via Northern Ireland.

Fresh tensions then flared in August after the anti-immigration riots in England and Belfast that resulted in more than 1,000 arrests.

The British minister for border security and asylum, Angela Eagle, said the government would not stand by and let people smugglers risk people’s lives on the back of false hopes.