The Schengen zone includes 22 member states as well as Norway, Switzerland, Liechtenstein and Iceland. But one unnamed Schengen country has refused to participate.

Latin for "laws of the elders", Mos Maiorum’s objective is to seize and possibly deport people without proper documents in an intelligence gathering exercise which the EU presidency says is necessary to “identify, prosecute and disrupt organised crime groups.”

Police will be required to fill out colour-coded forms of those intercepted. A red form is for people caught at the external borders and a blue form for those intercepted inside the Schengen states.

Details such as age, nationality, date of birth, place and time of interception, means of transport, migrant routes and asylum applications, if any, will be included. Fake documents will be seized.

Police will also try to obtain information on how much money a migrant has paid to enter the EU, their final point of destination, and the names of people who may have helped them along the way.

The operation was revealed when an internal EU document was leaked to press.

It follows statements made last week by Angelino Alfano, Italy’s minister of interior, when he announced an imminent end to the Italian-led naval search and rescue operation Mare Nostrum.

Mare Nostrum is credited with saving over 100,000 boat migrants since the start of the year. But a separate and much smaller EU-led operation Triton will take over with a primary mandate to carry out border surveillance.

The new Mos Maiorum police crackdown is co-ordinated by the central directorate for immigration and border police of the Italian ministry of interior along with the EU’s border agency Frontex.

Frontex itself was quick to distance itself.

In a carefully worded statement, Frontex executive director Gil Arias Fernandez said the agency “would like to stress that it has not had any role either in the planning or in implementation of this operation.”

Fernandez noted it only provides the Italians with statistics and data analysis of migratory flows.

“Its [Mos Maiorum] goals and way of execution is of ‘intra-Schengen’ and ‘police co-operation’ nature, which are not within the mandate of Frontex,” he said.

Estimates suggest there is anywhere from 150,000 to 450,000 people without proper documents are in the EU.

Thousands are likely to be people and families that have fled war-torn Syria and oppressive countries like Eritrea.

“Only a minority come with a visa valid for entry to the European Union,” said German Green MEP Ska Keller.

Mos Maiorum’s final results will be discussed by the "Working Party on Frontiers", a special committee in the Council – representing member states – on 11 December.