Immigration has boosted the population of the UK by more than one million since 1997, a think tank has warned.
There is little agreement over the reliability of immigration figures
Migrationwatch based its figures on the government's recently-released mid-year population estimates.
It said migration, along with children born to migrants in the UK, accounted for 81% of population growth.
But the Immigration Advisory Service lobby group said the figures were "utterly meaningless" and that many thousands were also leaving the UK.
And the Home Office noted that many immigrants were here temporarily, partly to study and also for business.
Migrationwatch drew the figures of growth in population of over 1.2 million (1,075,000 excluding British-born children) between mid-1997 and the middle of last year from research done by the Office for National Statistics and the International Passenger Survey.
The group said its figures did not include those who overstayed visas, or entered the country clandestinely.
It said, assuming that this category of migrants numbered at least another 30,000 a year, the total population rise would be two million over a decade.
But the Home Office said any such forecasts were highly speculative.
Migrationwatch chairman Sir Andrew Green said: "It is now self-evident that the failure to integrate our immigrant communities has brought us to a crisis in community relations.
"The government trumpet the recent fall in asylum numbers but other forms of immigration are now running at five times the level of asylum claims.
"We have reached a milestone. It is now essential to reduce the scale of immigration if we are to have any hope of achieving a reasonably integrated society."
But Keith Best, of the Immigration Advisory Service, said the figures were "extremely mischievous" and it was not known whether the UK was a country of immigration or emigration.
He said the statistics did not take into account the large numbers of people who left the country permanently every year, the large number of foreign students who came to study in the UK or the small sample used in the International Passenger Survey.
But Andrew Dennis, head of research at Migrationwatch, said that although using a small sample, the survey was reliable and was the only way of gauging net migration.
And Mr Dennis said that students would not affect the figures excessively as they would then appear in the departures column three years later.