The way we were: 100 years of the British census

A century ago, the first truly modern census pried into domestic life. As questionnaire time rolls around, Clare Dwyer Hogg explores how the face of the British household has changed

On Sunday 2 April, 1911, families across the country completed long and detailed questionnaires about their living conditions, occupations and fertility in marriage – making that year's census the most detailed, some might say intrusive, since records began. "It was a radical departure from what had come before," says Audrey Collins, a family history specialist at the National Archives. For the first time, the census asked questions about marital fertility, and the nature of occupations.

Over eight censuses since, taken at decade-long intervals – with the Second World War putting paid to the planned 1941 census – the Office of National Statistics (ONS) has amassed a body of a documentation that, taken as a whole, records the growth of a nation. But along with recording history, the census also records a moment in time, just as a camera does. Its questions demand to be f answered there and then – if two members of your 'household' on the night of the census are just weekend house guests, they are forever recorded at your address. This year, the 2011 census will appear on our doormats in time for the big form fill-out on 27 March – and it's set to look very different from its predecessors.

In the run-up this month, you might, for instance, come into contact with a big purple double-decker bus, windows painted over, like some kind of benign ghostly transport vehicle. It looks like this because it brings the future: "Help tomorrow take shape", says the big, friendly font on the side. The bus, an appointed spreader of information and answerer of questions, started at the foot of Tower Bridge, within spitting distance of the Mayor's tiered office, and is destined to travel across the nation. The message is to nobody in particular, because it's a message to Everyman, telling all of us that there's something compulsory approaching. Filling out your census form is a completion of a statute of law, with refusal punishable by up to £1,000 (although of the three million who refused to play ball in the last census in 2001, only 38 were prosecuted), but the big purple bus drives the message home that as the national census swings round again, it's going to take all of us to pull together.

1911 was the first year the original, hand-written household schedules were preserved, rather than copied into summary books by officials and then destroyed. The process of conducting a census has become a great deal more glitzy since those days of ink-stained toil; 2011 is the first year that we can participate in our civic duty online via a jazzy website, with a countdown clock, in case you're excited about the whole thing. The razzmatazz of the campaign that rolled out last month, a collaboration between the ONS and the Bray Leino advertising agency, is perhaps a symptom of the need to lean heavily on advertising and visual stimulants (ref: purple bus) to alert us all to what the government wants us to do and encourage compliance – but also partly because a lot of people will miss the adverts if they're written in English. The census form has been translated into 56 languages this year, and ethnic minority television channels, as well as temples, mosques and churches, are running awareness ads. It's a very modern thing when a census reaches a projected cost of £480m, and 35,000 officials are employed to carry it out.

The facts and figures gathered by such officials are said to be instrumental in the process of channelling £100bn of central government money to public services: schools, f hospitals and transport links will all – cuts permitting, presumably – emerge from this avalanche of statistics that will be released for public consumption in the summer. What's already known is that in the last 10 years, since the previous census, there's been as much growth in the population as there was in the three decades before – that's around 3.5 million. Immigration has been a major cause of this explosion; hence the new questions – in the section on ethnic groups, there will now be categories to tick if you consider yourself a 'Gypsy or Irish Traveller' or 'Arab'. A far cry from the solitary question about birthplace in the 1841 census, which asked for a 'yes' or 'no' to being born in Great Britain – if 'no', you simply recorded an 'F', for 'born in foreign parts'.

Religion is, of course, a divisive topic, and it's partly this which is raising cries of intrusiveness from detractors (the Conservatives, before coming to power, had denounced the census as 'invasive, intrusive, unsuitable', but there are no signs that they have changed it significantly). Although, of course, just because it's a legal requirement to fill out the form, it doesn't mean people will tell the truth.

The census of 2001 was the first to ask a compulsory question about religious belief, and around 390,000 people filled in their chosen faith as Jedi Knight (a chain letter had done the rounds). As a result, 'Jedi' is, officially, the fourth largest reported religion within the UK. Perhaps that said as much about the attitudes within Britain then as the numbers of Sikhs and Christians did. Either way, the new questions this year, including one asking who enjoys 'same sex civil partnership status', are as much a reflection of the time.

All the data taken since 1911 remains in the custody of the ONS – privacy laws mean information is only released 100 years after the census. But even without the aid of statistics, looking at the photographic evidence of different households at the census times since then, what's immediately obvious is how sparse the homes are in which many lived.

Our notions of poverty have changed, but so has our sensory environment. As recently as 1991, people weren't surrounded by technology, crowded out by virtual ways to communicate, or bombarded by hundreds of flashing images on television, phones, and laptops, all advertising, say, the onset of a new census. Poverty comes in different forms these days; not least socially and culturally. But then, of course, it would be hard for a questionnaire to work that one out, big purple bus or no.