First question on the census form: is there any point to it?

The victim was dressed as a Jedi knight at the time of the attack (Reuters)

Very soon it will be impossible not to know that 2011 is a census year. The public is to be bombarded with advertisements warning them they will have to fill in a form, saying who was sleeping where on the night of 27-28 March.

Three weeks before census day, the questionnaire will be available online, and copies will fall with a thud through the letter boxes of 25 million households, because this year's census form is bigger than ever – 56 questions filling 32 pages.

The scale of the operation has invoked protests from civil libertarians, who think it is intrusive, and Tories, who think that, at £486m, it is costing too much.

Francis Maude, the Cabinet Office minister responsible, has hinted this census could be the last, and the Government might not have gone ahead with it at all if they could have cancelled it without running up excessive costs, but too much preparation had been done before they came to power to make that possible. Mr Maude believes that most of the information collected during a census is already available from other sources, and there may be a cheaper way to fill in the gaps.

Daniel Hamilton, campaign director of the civil liberties group Big Brother Watch, denounced the whole exercise yesterday as "a monumental waste of time and money". He added: "At 32 pages, the census includes intrusive questions on your proficiency in English, your health, when you last worked, the identities of your overnight guests and the type of central heating you have. The Government has no need and no right to know this information about you.

"Last time, 390,000 people declared their religion as Jedi. There's no reason to think people will take the census any more seriously this year."

However, others defend the census as a unique and valuable tool. Businesses who want detailed information about where to find potential customers say there is no other database to rival it. It is also used to plan housing, health care, schools, and other services.

And the Office for National Statistics (ONS) has promised that the personal information gleaned will be locked away for 100 years without being shared with any other agency. They say that illegal immigrants or escaped prisoners on the run can fill in their census forms without fear of detection.

But if you groan inwardly at the sight of those 32 pages of questions and think to yourself: "Do I really have to fill this in?", the answer is yes. It is a criminal offence, punishable by a fine of up to £1,000, to refuse to complete a census form.

Prosecutions are rare, because the ONS is more interested in persuading people to comply than in dragging them through the courts. Last time 38 people had heavy fines inflicted on them for non-compliance, and one went to prison for refusing to pay.

From early April, compliance officers will be chasing up households that have not returned a form, and towards the end of the month they may start collecting evidence for criminal prosecutions. In a separate exercise, canvassers will contact about 250,000 households to question them face-to-face to get an idea of the accuracy of the census.

What the statisticians cannot do is prosecute those who treat the question on religion as a joke, and enter "Jedi", as nearly 400,000 did 10 years ago. Glen Watson, ONS census director, said yesterday: "The religion question is the only voluntary question on the whole questionnaire. We would process the information and we would include that in the results, I imagine."

History of the census

1086: Two decades after conquering England, the Norman rulers were still paying Danegeld and William the Conqueror ordered a tax survey. To the villagers, it was like being questioned at the Last Judgement. The Domesday Book, with details of 13,418 settlements, is kept in the National Archives in Kew.

1801: The British authorities took fright when the demographer Thomas Malthus published an essay in 1798 suggesting the population was growing so rapidly that food would soon run out. That prompted the 1800 Census Act and the first official census on 10 March 1801. Most of the data has been lost.

1841: The Victorians were brilliant bureaucrats. They pioneered the census form that was delivered to every household to be filled in on the night of Sunday, 6 June 1841. This system, which is still used, produced the first census that is of real value to anyone wanting to trace their family history.

1951: This was the first census for 20 years, because none were taken during the Second World War. There were 24 questions, compared with 15 in 1921. Women under 50 had to say when and how often they had been married. Problem pages were full of letters from women who feared details would be made public.

2001: With 41 questions, it was the biggest census form yet, the one that met the greatest popular resistance, and the first to feel the power of the net. Encouraged by a mischievous email, 390,000 people gave their religion as "Jedi". The authorities may have been annoyed by the jape, but it did not break the law.

The Census in numbers

21 The number of times the British will have been counted since the first census in 1801

56 Number of questions on the 2011 census form

25 million households will be surveyed this year

£486m The estimated cost of the 2011 census

35,000 Number of census field staff employed by the Office for National Statistics

38 people successfully prosecuted for refusing to fill in 2001 census