Most observers believe that immigration is at historically high levels and that pressures on Britain's border controls are likely to grow.
But because no one knows how many immigrants are smuggled in, or how many temporary residents stay on illegally, nobody can calculate authoritatively the numbers of foreigners who move to this country.
An equally impossible challenge is predicting as Migrationwatch UK has attempted to do what will happen in the next few years, let alone 10.
The organisation cites Home Office figures predicting that a net annual figure of 180,000 non EU-nationals, including asylum-seekers, will be allowed to stay in the country. In coming to its prediction of two million immigrants over 10 years, Migrationwatch UK alludes to another report for the Government two years ago, which commented on the "unusually higher net migration levels of the last few years". It said the long-term trend was likely to be upwards as migrants won the right to bring their families to Britain and as established ethnic-minority communities attracted new arrivals.
But the Home Office refused to endorse the statistics yesterday, putting the figure for non-EU immigration at closer to 135,000 a year. The Home Office said the total had dropped sharply because of faster, and more effective, procedures for returning failed asylum-seekers.
It said the figures should be treated with cautionbecause they included British citizens returning after spending time abroad and migrants, such as students, who would eventually return to their native country.
Keith Best, director of the Immigration Advisory Service, said Migrationwatch had included in its figures asylum-seekers who had been given permission to remain for a temporary period and those who were appealing against their failed applications. Both categories of people would probably eventually leave the country, he said.
Migrationwatch UK also calculates that each year 35,000 legal visitors stay on illegally and another 25,000 make their way into the country undetected. But Mr Best said those estimates were a mere "shot in the dark" and criticised the figures on illegal entrants.
He said: "Migrationwatch just don't know how many people come in the back of a lorry; the Home Office removes about 10,000 or 11,000 a year. Depending on your political view, you can either say that is the tip of the iceberg, or you can say that is the totality."
Habid Rahman, chief executive of the Joint Council for the Welfare of Immigrants, des-cribed the figures as "flawed and alarmist".
He said the past few years had been exceptional because of conflicts in the Balkans, Somalia and Afghanistan putting pressure on Britain.
Mr Rahman said the suggestions of a continuing population boom were undermined by the fact that the British headcount remained steady in the latest census.
Register for free to continue reading
Registration is a free and easy way to support our truly independent journalism
By registering, you will also enjoy limited access to Premium articles, exclusive newsletters, commenting, and virtual events with our leading journalists
Already have an account? sign in
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies