Since 1997, record levels of immigration have boosted our population by more than 2 million, accounting for half the total estimated rise in population of about 4 million.
So is Britain getting full?
With immigration projected to drive two thirds of our population growth, the polls suggest voters think the answer is "Yes".
Next to the economy, immigration is the second most important issue, beyond even crime and the NHS.
In last week's televised election debate, all three main party leaders said they would be tough on immigration.
The Office of National Statistics say that over the next two decades the UK population is on course to grow by eight million to 70m.
That is roughly the equivalent of adding eight new cities, each the size of Birmingham.
Quality of life
If that happens it will have profound implications for public policy: England expects to take 90% of that growth. Yet, aside from Malta, England is already the most densely populated country in Europe, according to UK and UN statistics.UK POPULATION STATISTICS
Where will all the new houses and shops be built?
And from where will come the tens of billions to build the infrastructure - the sewers, water treatment plants, power stations, railways lines, roads, schools, and hospitals?
This, at a time when we are about to enter one of the most deep and sustained periods of public spending cuts in our history.
Most of the new homes are needed because more people are living longer or alone. But four of out of every 10 new households will be accounted for by immigration - the only factor amenable to government control.
How might our quality of life be affected?
Many of us could end up feeling distinctly squashed - new houses being built today already have the smallest dimensions in Europe.FIND OUT MORE...
The average commuting time to work is now among Europe's longest. That is likely to grow as the number of households forming continues to out pace new home completions, driving up the price of properties and forcing people further from major towns and cities.
For families not able to buy or rent privately, our growing population and the mass sale of the most desirable socially rented homes have contributed to an acute shortage of council housing.
In the London borough of Barking and Dagenham, up to 600 families compete for every three-bed home that becomes available.
Katy Thorndike has been on the waiting list for more suitable accommodation for herself and her five children for five years.
Her flat is riddled with damp and when it rains she says the carpets squelch.
She was born and raised locally but she believes migrant families have been getting preferential treatment.
"We do see a lot of migrants coming into the borough and getting the properties straightaway, " she said. "I do think it's unfair. I'm stuck in a slum like this."
The far right BNP is challenging here, in what has been a traditionally safe Labour seat.
Miss Thorndike said she will not be voting BNP but added: "I'm not a racist, each to their own, but I do think that maybe people from this borough should be given preference over people who are not."
Barking and Dagenham council insist migrants do not get preference over housing allocations.
But inevitably, increased numbers of migrants lengthen the queue, resulting in increased competition.
Since we interviewed Miss Thorndike and her family, Barking and Dagenham council have rehoused them.
Across England, there are now 1.8m households waiting for social housing.
Schools are also feeling the stress from our fast growing population.
At Mount Carmel Primary in north Manchester head teacher Patricia Ganley has had to turn her office into a classroom.
"There's been a big explosion of people coming into the area," she said. "We've had a lot of families from overseas."
How many marks out of ten did she give the government for planning? "About a two or three" she answered.
Across the UK, births are up by 11% since 2004.
At North Manchester General Hospital, Denise Woods, Community Midwifery Matron, said 2,800 women are giving birth a year - an increase of 600 a year from 2002.
A higher birth-rate among new immigrants is contributing significantly to this rise.
In England, one in four births - 170,000 a year- is now to a mother born abroad.
However, immigration minister Phil Woolas does not give the ONS population projection much credence.
"I don't believe we will get to 70m" he said.
The government has no control over EU migrants.
But Prime Minister Gordon Brown has insisted that the government's new points based system allowing in only economic migrants and students from other countries who score sufficient points through their skills, jobs and financial status is reducing net migration.
ONS projections do not take account of such changes in government policy.
On the other hand, its recently retired head Dame Karen Dunnell says: "We have actually greatly improved the quality of statistics over the last five years."
The latest finalised ONS statistics - for 2008 - do show a fall in net migration from 2007. But since then immigration has still added around 300,000 to the UK's population.
So what are the differences between Labour and the Conservatives? Not, perhaps, as sharp as Mr Brown and Conservative Leader David Cameron might wish voters to think.
The Tories say they will impose an overall cap on the number of work permits wherever they impact adversely on public services. Yet that limit may not, in practice, be very different from the numbers allowed in by Labour.
Shadow immigration minister Damian Green said: "I do think government should control that. I think the immigration rate should be substantially lower than it has been under the current government."
But he declined to give a figure on what the work permit cap should be, except to say that net migration - the difference between immigration and emigration - would be cut from the current 163,000 to "tens of thousands".
Under both Labour and the Conservatives, permits are likely to be dictated primarily by the level of skills shortages in the economy as independently assessed by officials.
Where does all this leave the ONS projection of 70 million?
Chris Huhne, the Liberal Democrats home affairs spokesman, said the fact that Thames Water is having to build a desalination plant in the Thames Estuary to increase the water supply vividly demonstrates how the population of London and the South East are "reaching clear environmentally sustainable limits".
Even so, for Mr Huhne the issue is not whether the UK reaches "65m, 70m (or) 75m".
What matters is how migrants are distributed across the country, he said.
The Liberal Democrats under Leader Nick Clegg, he said, want to restrict them to less densely populated parts of the north and Scotland to help rebalance the economy away from the south east and financial services towards more traditional forms of wealth creation, such as manufacturing.
By contrast, Phil Woolas said: "I don't think our country could cope easily at all with 70m."
Given the vicissitudes of the economy, precisions by any of the parties about the annual reduction in net migration is not possible.
But to avoid getting to 70m, the reduction will have to be substantial - down from 163,000 to, at most, an average of 50,000.
Whichever party wins the election, the ONS population projection will present them with an acute dilemma - without substantial falls in immigration, house prices and rents will go yet higher, increasing the divisions of an already deeply divided society.
The alternative is a massive building programme. But that would mean borrowing even more at a time when national debt is already at record levels. Politics is, indeed, about tough choices.
Panorama: Is Britain Full? BBC One, Monday, 19 April at 2030 BST and then available in the UK on the BBC iPlayer.
Barking: Full candidate list