Somewhere in Trafford Park, Greater Manchester – we are not permitted to say exactly where – a vast windowless warehouse, with a footprint the size of 64 tennis courts, is preparing for an awesome IT project.

For a few frenetic weeks later this year, 1,300 carefully vetted temporary staff will be working flat out in this high security facility. Their task: to capture digital data off as many as 25 million census questionnaires and then shred those forms.

A national census has been carried out in Britain every decade since 1801 (apart from 1941). This one, in March, will be Britain’s 21st, a nationwide data trawl costing £482 million. It will net around three billion facts from the data thumbnail every one of us must supply.

Each of us is legally bound to answer up to 42 detailed questions about ourselves and, if we are head of a household, 14 questions about that household. Nothing to be paranoid about, say the number crunchers at the Office of National Statistics.

Statisticians insist secrecy protocols will protect our sensitive personal information

Au contraire, every reason be paranoid and suspicious, claimed the pressure group Census Alert in 2008, fearful of our personal data leaking to the US government. It tried to stop the ONS awarding a £150 million data capture contract to Lockheed Martin, the American defence and security giant.

Statisticians at the ONS are wary of such political debate. They insist secrecy protocols will protect our sensitive personal information for 100 years. So our answers won’t be released until 2111, to be picked over then by historians and genealogists hoping to shake black sheep out of family trees.

The ONS says bullishly: “We are bound by law to respect individual rights to confidentiality and have a 200-year track record of maintaining census confidentiality.” Information is not shared with any other government departments or marketing companies, it adds.

Operational sites like the Trafford Park centre are very secure and “will have access control systems, CCTV, security guards and intruder alarms to prevent unauthorised access to premises, documents and other confidential files”, says the ONS.

Yet in these days of sophisticated data mining, of refining golden nuggets from mountains of freshly dug facts, the 2011 census information provides a priceless database. Which is why, after all, governments undertake such exercises on a regular basis.

“The primary purpose of the census,” explains the National Statistician, Gil Matheson, “is to produce accurate population estimates. These will underpin a myriad of important funding and planning decisions during the next decade, at national and local level.”

The latest British census is, arguably, the nosiest ever undertaken

Fair enough. But the form of Britain’s census is mutating over time. The early ones were little more than a simple head count, or poll. The earliest, the Domesday Book, collected data about land and livestock as much as villeins and peasants, to establish how much tax the king could wring from his subjects.

The latest British census is, arguably, the nosiest ever undertaken. It has dropped four questions – on heating, bathrooms, basements and workplace colleagues – but it has added nine new ones. Three of these seem harmless enough, asking about number of bedrooms, types of central heating and visitors staying in the house on the night of the census.

But the other six are much more probing. If you have a holiday home in the Seychelles that the taxman doesn’t know about, beware. The fourth new question expects people to fess up to second homes. And then there are what might be called the five immigrant questions. Though the ONS promises “there are no questions that distinguish between legal and illegal immigrants” (who would willingly tell the authorities they are an illegal?) the 2011 census is clearly trying to sharpen up the demographic picture of immigration with five new questions.

These ask about the language you speak and your proficiency in English, the month and year you entered the UK, your intended length of stay, the passport(s) you hold, and your national identity. These seem aimed at immigrants, asylum seekers and guest workers as well as foreign students and tourists.

But if these questions seem intrusive, spare a thought for the citizens of India. There, 2.5 million census wallahs start counting in February. Not only will Indians be asked which caste they belong to, they will also have their photo and fingerprints taken – to be stored forever on a biometric database.

Photo: The last UK censusin 2001.

The hidden ones

The 2011 census by the Office for National Statistics will be a very democratic business: from rough sleepers to royals and their flunkeys no one can escape its all-seeing eye.

Every person in every household, every prisoner in jail or soldier in barracks, every patient spark out in intensive care, every student in digs, every citizen, young and old, will have their details recorded. In theory, that is.

It’s not easy to count those who sleep rough

Just one niggling problem, one that has frustrated census-takers since the time of the pharoahs: how to make sure everybody gets counted? Census managers know that plenty of folk, the multitudinous “hidden ones”, slip below the radar.

Rough sleepers are one obvious group. Margaret Barrett of the ONS says: “Let’s not beat about the bush – this is a massively complex task. It’s not easy to count those who sleep rough, the homeless or those who have no fixed abode and often move from place to place.”

In 2001 census collectors walked, somewhat aimlessly, around streets trying to count as many homeless as possible. This time, says Barrett, the approach is very different. Working closely with the umbrella body Homeless Link, collectors will be stationed in day centres and hostels.

This year’s local authorities’ street count – plus estimates – calculated there are around 1,200 rough sleepers in England, which some believe seriously underestimates the true numbers. The hope is that the 2011 census will give a better fix on this statistic.

“We are doing everything we can to make sure homeless people have ample opportunity to fill in their questionnaires,” says Barrett, adding that “my role is to engage with hard-to-contact groups, to ensure as many people as possible take part in the census”.

But rough sleepers are just the tip of the hard-to-contact iceberg. The ONS reckons that the coming census “will probably show the most rapid and dramatic social change in any decade ever”.

Much of this change involves the ethnic patchwork of the nation, which is why the ONS planners are working so hard to involve ethnic minorities in the census, particularly the young amongst them. Grime star Ghetts (below) has been enlisted, making a track, Invisible, about getting your voice heard.

The track is free to download (www.invisible2011.com) and Ghetts says: “The point is that young people are the future. We’ve got to take every opportunity to get our views across so that we get the kind of communities that we want for our own kids.

“Too often ethnic minorities are ignored. Unless we fill in the census our needs are invisible. This gives us the chance to shape the future of our neighbourhoods. It’s time to stand up and be counted.”

In another outreach effort, the ONS’s Then and Now photo competition encourages people to send in two photos and 250-500 words on how their family has changed over the years. It’s at http://2011.census.gov.uk/
2011thenandnow.