How do you solve a problem like a rising population? And, if it is a problem, what type of problem is it.

That is a debate immediately being sparked by the first results from the 2011 census, revealing that the population of England and Wales is now 56.1 million, rising by 3.7 million (7%) since 2001. That is the largest growth in any 10-year census period since this began in 1801.

This is not the whole census, which is released in stages, but the totals by gender and region. We will have to wait until November for a full breakdown covering , race and migration. Even the total UK population of remains a little speculative, as the Scottish census is not complete and nor is that from Northern Ireland, so working out a British or UK-wide total of around 63 million from today's release depends on using best estimates from past projections.

Should we worry about a rising population - and, if we should, what should we do about it?

The more benign view is that this is, at worst, a problem of success, and a challenge which the most successful advanced societies - such as America and Germany - have faced for many years.

Given a choice, the problems of depopulation, of mass emigration, demographic imbalances and even falling life expectancy experienced by struggling societies like Russia, or feared by those like Greece who are worst hit by the economic crisis, are considerably tougher than the pressures of managing a rising population.

Something similar can be true at a city level: it is London that has seen the largest population increase, now up to 8.2 million from 7.3 million. The north-east has both the smallest population of any region, and saw the smallest increase, of just 2%. There were declines in population in the last decade in Sunderland, South Tyneside, Redcar and Cleveland and Middlesbrough.

On this view, Britain should welcome aspects of a rising population, such as increased longevity (with 430,000 people aged over 90) and improved health, and probably broadly welcome the (now ending) baby boom of the last decade - so that we have 400,000 more under fives than there were a decade ago (now 3.5 million) for its contribution to greater demographic balance. After all, we also have more over 65s than ever before, with the proportion reaching a record level of 16.4%.

This would also involve putting in place a system for managing immigration which reflects Britain's interests and values, in how it chooses from those who wish to vote with their feet and come in to contribute to our economy and society, seeking to manage the gains and pressures, while remaining open to business, culture, study and tourism. Net migration is estimated to contribute just over half of the increase. From this perspective, the key population policy issue is not about whether the total is 63 million or 66 million, but how the churn of a liberal society is managed for the public good.

Other voices want to raise the alarm about a rising population - and ensure that we call a halt to it.

It is, though, worth trying to work out whether the worry about population is really about population or not.

For a pressure group like Population Matters, it really is population that matters. The clue is in the name. But the organisation was not always called that. Its previous title - The Optimum Population Trust - did tend to lead to the question: what would the optimum population be?

Population Matters think the answer for Britain is 20 million.

That seems a little impossible, though the public briefings point out that Britain has had a lower population before, and that this was only 10 million at the time of the Act of Union between England and Scotland in 1707.

Alex Salmond will hold a referendum on the Act of Union itself, but few expect this to provide an opportunity to turn the clock back to the 18th century more broadly.

This all begins to sound rather worrying, but Population Matters are keen to offer reassurance. They wouldn't slash the population by two-thirds in one or two Parliaments. They would gradually manage it down by 2.5% a year, with a strategic policy of national contraction. The social pressure on parents to volunteer to "stop at two" would be purely voluntary, its advocates stress, though that may depend on what the social stigma feels like. Such measures would take centuries to reach the goal.

Those who want a 20 million population are making common cause with those who have a more modest goal, campaigning under the slogan "no to 70 million". The success of the pressure group Migration Watch in securing 100,000 signatures on an e-petition, means that the proposal for Britain capping the population will be one of the first things that MPs debate on their return from the summer recess, with the debate having been scheduled for Thursday 6th September.

The real concern here is immigration - with population being used as a slogan. Its advocates will cheerfully admit they have plucked the number from the air, as a campaign slogan, rather than basing it on any research.

It is good for parliament to debate the population question. But any grown-up debate needs those proposing a population limit to tell us where they would set it, why, and what they would be prepared to do to keep the population below it.

The petition does not do that - it declares that the government must take "all necessary means" to make sure immigration is cut to keep the population below the limit, but with no information on what the necessary steps are.

The government's dilemma is that it is already missing one target - to cut net migration to 100,000 a year. Ministers might wonder whether those advising them to respond to missing a target by setting a much harder one is going to be helpful. Impossible promises don't improve trust; they further corrode it. And the steps to reduce net migration involve specific steps

Many people will worry about being asked to sign up for a blank cheque to limit the population without even being told what that's going to mean - for jobs, universities and care homes, to whether

If MPs don't want a population limit, then they should work out how to address concerns about population. The sensible alternative to an unworkable and arbitrary limit is to manage population changes better, government should respond more quickly to change than in the last ten years, not relying so much on a decade-old census but using up-to-date information like school rolls, so that the resources go to where we need it.

Instead of declaring Britain closed, we should spread growth and jobs around Britain, just as we've regenerated Stratford to host the Olympics, and turned around the population decline in the centre of great cities like Manchester and Liverpool.

Sunder Katwala is the Director of British Future

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