More than half of all marriages in the Republic between men from outside the EU and non-Irish EU women in recent years are believed by gardaí to have been bogus.

The rates of such marriages have fallen so much since the Garda-led Operation Vantage began 18 months ago that senior officers now believe the abuse of the system was much more widespread than previously suspected.

There has been a near 60 per cent decline in notifications to marry from couples comprised of a non-EU national and a non-Irish EU national.

Gardaí believe hundreds of men, typically from India, Pakistan and Bangladesh, came to Ireland in recent years with the intention of getting married to a woman from one of the other 27 EU states, usually one in eastern Europe.

Once declared man and wife under Irish law, the men could apply through their spouses to secure EU treaty rights, enabling them to live and work anywhere in Europe for the rest of their lives.

Even when couples separated, the men would retain their EU passports and all the rights that came with it.

Asylum

Most of the men applied for asylum when they first arrived in Ireland. Gardaí believe they were doing so to give themselves time to organise their bogus marriages.

Officers also believed the asylum claims were intended to convince the Irish authorities they had met their would-be brides legitimately in Ireland while waiting for a decision.

The abuse had become so large-scale that since Operation Vantage began, not only have marriage rates plummeted, but spikes in asylum claims had been reversed.

In the first eight months of last year, there was a 58 per cent decline in notifications to marry from couples comprising one non-EU national and one non-Irish EU national; from 1,175 to 497.

“Certainly now, almost 18 months on, when you look at how all of the trends have changed so much, you really do see the extent of the abuse that was going on,” said one justice source.

There has been a 66 per cent decline in the number of applications by Pakistani men to marry in Ireland.

And the number of Pakistani nationals applying for asylum fell by 83 per cent from 1,306 applications in the first 11 months of 2015 to 228 in the same period last year.

Since Operation Vantage began, there has been a 73 per cent reduction in the number of Indian men applying to marry in Ireland and an 88 per cent reduction among Bangladeshi men.