The one-day operation, codenamed Mermaid, will be staged by 52 police forces in conjunction with immigration officials, benefits agency inspectors and customs officers, who will be waiting at the roadside to question suspects.
Disclosure of the mass road-blocks has angered civil liberties groups, who said such tactics were a "gross invasion of privacy". Liberty said it was looking to bring a legal test case to show that such questioning could be unlawful. Liz Parratt, a spokeswoman, said people could not be compelled to answer questions from other authorities after being stopped by police for road-safety checks.
But, she said: "Most people won't know what their rights are when they are being questioned and will be far too alarmed or scared to refuse. We would be happy to advise anyone who has been a victim of this abuse of power."
In a smaller version of the operation in June, 1,098 vehicles were stopped and 113 people who said they were on their way to work were found to be in receipt of unemployment or sickness benefit. The operation is believed to have saved pounds 176,000 in false benefit claims.
A benefits agency spokeswoman said the tactic was extremely successful. "The police officer will stop the vehicles and our fraud officers will ask the people for their name, national insurance number and any benefits they are claiming."
Operation Mermaid, which is backed by the Association of Chief Police Officers, began in 1995 and has mushroomed as more police forces have recognised its effectiveness in trapping dangerous vehicles. This year, all forces in England, Wales and Northern Ireland will take part in the exercise with an unprecedented amount of support from other government agencies.
It is co-ordinated nationally by a West Midlands police traffic intelligence officer, Bob Nockalls, who said the road-blocks should properly be called "road checks". PC Nockalls said the fears of civil libertarians were unfounded and that Mermaid "will remain a road safety operation". He added: "People are in no way detained for anything other than road traffic matters. While they are in that check then people like the benefits agency will speak to the occupants. Nobody can make anybody speak to the benefits agency."
Police argue that the presence of immigration, customs and other officials is essential to the efficiency of the operation. Police officers finding evidence of other criminal activity are obliged to act, and if illegal immigrants or contraband goods are found in a vehicle then the other agencies can be quickly called in while police continue with safety checks.
It is hoped that all drivers who are stopped can be dealt with in half an hour.
PC Nockalls said: "The great majority of people we check are perfectly legitimate people."
Random Mermaid checks are carried out by local forces at different times of the year. In total, 93,000 drivers have been stopped, leading to 673 arrests and 5,500 vehicles being banned from the road. On one occasion, a rocket launcher and ammunition were recovered.
One recent exercise in Surrey by the Metropolitan Police led to eight arrests, of which five were for immigration offences. One man was arrested for giving false information to police, another was in possession of an offensive weapon and another was the subject of an arrest warrant. Thirty- five of the 404 drivers stopped were reported for benefit fraud, 27 vehicles were banned from the road, and 112 drivers were fined for having invalid tax discs.