Details of the way a website carrying the 1901 census was "overwhelmed" by demand have emerged in a report from the National Audit Office.
The 1901 census website is now up and running
The site had to be withdrawn five days after its launch in 2002 after visits from around 1.2 million users an hour.
The site was reopened seven months later and now caters for between 8,000 and 10,000 internet users every day.
The National Archives must learn the lessons from the episode if it puts the 1911 census online, the report says.
It says the level of interest in the website had not been expected by the Public Record Office (PRO), which had "developed a pre-launch strategy based on a low key launch".
The report says the PRO was taken by surprise by the level of press interest in the site, while launching it during a holiday period meant more internet users were able to access it from home.
The website was launched on 2 January 2002 with the aim of catering for a maximum of 1.2 million users in a 24 hour period.
However, just three hours after being launched, by noon 1.2 million users per hour were trying to access the site - with the same level of demand continuing during the next few days.
The report says this demand "overwhelmed the site" and led to the PRO and its contractor, QinetiQ to close it and launch an investigation.
As a result, the site was closed until reopening on a limited basis in August 2002, before being made fully available in November the same year.
The report says the site has operated effectively since reopening. It has generated gross revenues of £4.5 million in the period up to 31 October 2003 through charges for detailed information.
NAO head Sir John Bourn said: "The project to provide online access to the
1901 Census was ambitious and, ultimately, successful.
"In implementing the project, the Public Record Office and its contractor
QinetiQ encountered a number of problems which they managed to resolve
"Looking forward, the National Archives should also consider these lessons if
it decides to provide online access to the results of the 1911 Census."
The report also examines the failure of a plan to use prisoners to computerise the census entries.
The transcription of 32.5 million
records including those of the future Queen Elizabeth the Queen Mother and
Charlie Chaplin was subcontracted to Enterprise and Supply Services, a
division of HM Prison Service.
But insufficient progress was made, meaning the timetable for launching the site was put at risk.
The work was then subcontracted again at a cost of £1.8 million to companies based in India
and Sri Lanka as well as the UK.
The Prison Service said "painful lessons" had been learnt from the episode.
"In hindsight the
Prison Service overestimated its capacity to deliver both the quality and
quantity of work required," it said in a statement.
"Painful lessons have been learnt and procedures have been implemented to
ensure the same circumstances could not occur in the future."