The number of people migrating to the UK each year will be 45,000 more than previously predicted, according to official estimates.
The Tories say Britain's public services are overstretched
The Office for National Statistics (ONS) had estimated the net increase in population due to migration would be 145,000 a year.
But it has revised that upwards by about a third to 190,000 migrants annually over the next 20 years.
The ONS also predicts life expectancy will rise further than anticipated.
Sir Andrew Green, chair of Migrationwatch UK, said: "The result is that 86% of our population increase will now be due to immigration, which will add 7.2 million to our population between 2004 and 2031."
Shadow immigration minister Damian Green told BBC Radio 4's Today programme: "This involves a population of a city the size of Liverpool being added to our population every five years or so, and obviously our public services, our infrastructure, housing demand and so on cannot cope."
The Conservatives wanted "an explicit annual limit" on the number of people allowed to enter the UK, he added.
The ONS said the amended estimate was partly due to factoring in record net immigration in 2004 and 2005, mainly from eastern Europe.
Changes to the way migration figures were calculated also played a part.
Immigration Minister Liam Byrne said: "This report shows what could happen unless we take action now.
"Frankly, it underlines the need for swift and sweeping changes to the immigration system in the next 12 months.
"Migration is bringing new wealth but also new worries to Britain. That means we need to drive through radical action now to make sure our borders policy is fit for the future."
Nick Clegg, the Liberal Democrat home affairs spokesman, said: "Immigration is enormously important to Britain, but these figures highlight the need to plan for its impact instead of indulging in the usual mix of media-driven populism and administrative incompetence."
His party has proposed a "selective amnesty" for some illegal immigrants, making them eligible for citizenship after 10 years' residency.
Danny Sriskandarajah, from think tank the Institute for Public Policy Research (IPPR), said: "The challenge is to ensure we can continue to reap the benefits of migration at the same time as building cohesive communities."
Julian Bild, a senior lawyer for the Immigration Advisory Service, said: "Perhaps this isn't immigration as such, but EU nationals exercising the same rights that we have - which is unrestricted freedom of movement around Europe."
The ONS also predicts life expectancy for babies born in 2031 will rise to 82.7 years for males and 86.2 years for females, up from 81.4 years and 85.0 years in earlier calculations.
Estimates for how migrants would be distributed across the UK in years to come were also being revised.
England is projected to have 171,500 new migrants a year, over 40,000 more than previous estimates.
Scotland's new arrivals are put at 8,500 a year compared with 4,000 previously, while Northern Ireland's population is likely to rise by 500 a year rather than fall by the same number.
Conversely, Wales is now expected to receive 2,000 fewer new migrants overall than previously thought.