Population has grown by two million in six years

The statistics show an extra 388,000 people joined the country's population in the year to mid-2007, giving an increase of more than two million inhabitants since mid-2001.

The main reasons include a continuing surge in migration - accounting for 52 per cent of last year's increase - and a rapidly rising birth rate, mainly among foreign-born women. A slightly lower death rate is also contributing.

The rate of growth meant around one million people were being added to the country's population each year - the equivalent of a city the size of Birmingham - and was consistent with earlier projections predicting a population of 71 million by 2031.

The new figures, released by the Government Office for National Statistics, will fuel debate about immigration policies and call into question Home Office suggestions the rate of arrivals is likely to slow over the coming years.

Unveiling the figures, Guy Goodwin, director of population, health and regional analysis at the Office, said last year's 388,000 rise was the highest since records began. It meant the country now had a total population of 60,975,000.

He said the main cause was high levels of inward migration, with 605,000 people arriving in the UK in the 12 months up to mid-2007, compared with 406,000 existing residents moving out.

This gave a net influx of 198,000 people due to migration - 9,000 more than the figure for 2006, and a net gain of more than one million people through net inward migration since 2001.

Mr Goodwin said a rise in the birth rate - 84,000 more babies born last year than in 2001 - was also contributing significantly, but migration was again a key factor, accounting for births by foreignborn women. These represent two thirds of last year's increase in births.

He said the inflow of migrants into Britain was at the "highest recorded" level and added: "It translates into 1,650 people a day coming into the country."

Today's statistics also show a continuing-rise in London's population, which increased by 44,500 last year to give a new total of 7,556,900.

But the national net figure for inward migration masks an even larger influx of overseas citizens. Of the 605,000 migrants who arrived last year, only 75,000 were UK citizens returning, while the 406,000 figure for outward migration included 202,000 Britons departing the country. That represents a net exodus of 127,000 Britons over the year and a net influx of 326,000 foreign nationals.

The number of UK residents born abroad has hit 6.3 million - an increase of 1.1 million on 2004. About a third of the rise since 2004 is due to migration from Poland and other new EU members, but the largest number of the UK's foreign-born residents are from India.

Councillor Colin Barrow, Westminster Council leader, warned of problems accurately charting the population in London's hard-to-count areas like Westminster. He said: "The 2011 census could again miss large amounts of population in urban areas as it did in 2001 and future population projects critically undermined."