The cost to the taxpayer of abandoned Whitehall computer projects since 2000 has reached almost £2bn, not including the bill for an online crime reporting site that was cancelled this week, a survey by the Guardian reveals.

The failure of the multimillion-pound police site marks the latest chapter in the government's litany of botched IT projects, with several costly schemes biting the dust. Blunders overseen by Downing Street have included the much-derided £486m computer upgrade at the Child Support Agency (CSA), which collapsed and forced a £1bn claims write-off, and an adult learning programme that was subjected to extensive fraud.

Top of the ministries for wasting public money is the Department for Work and Pensions, which is responsible for squandering more than £1.6bn by abandoning three major schemes — a new benefit card which was based on outdated technology; the upgrade to the CSA's computer which could not handle 1.2m existing claims; and a £140m streamlined benefit payment system that never worked properly.

The Guardian's survey of abandoned projects is not exhaustive and the total of £1.865bn is likely to be a considerable underestimate of the actual cost to taxpayers because neither Whitehall nor the National Audit Office, parliament's financial watchdog, keep definitive lists of which schemes go wrong. Also it does not include the major modifications required to fix new systems that have failed to perform as required.

One example is the pilot work done on the new £12bn NHS computer system. Outdated technology was installed at Bexley hospital in south London, and it has had to be replaced after it was found to be "unfit for purpose".

Another example is the huge modification required to a new computerised single payments system for farmers run by the environment ministry Defra's Rural Payments Agency. The government has had to set aside about £300m to meet possible EU fines for making the wrong payments to thousands of farmers.

The abandoned police site, which was launched in 2003, allowed the public to report non-urgent crimes and provide photographic and video evidence through the internet. The system — linked to police forces around the country — then prioritised the information and distributed it to the correct forces.

It was being used to report about 30,000 crimes a year but began to falter when defence technology company Qinetiq was brought in to build a replacement in 2005. Costs began to spiral and the new system was deemed to be unfit for purpose, resulting in suspension of the service last March and closure in December.

The deal is now subject to a legal dispute, with Qinetiq claiming that it has completed the work it was contracted to do. The National Police Improvement Agency, which manages IT systems for the police, would not give details of how much money had been spent on the portal, but documents obtained under the Freedom of Information Act showed that running costs had risen above £5m a year in 2006.

The replacement system was not fit for live use due to "a range of serious defects and delays," a spokeswoman said. "It is not possible to issue more details as it is now subject to legal proceedings."

Earlier this year, one senior Whitehall official called into question the heavy spend and high rate of failure.

Joe Harley, programme and systems delivery officer at the Department for Work and Pensions, said the government's £14bn annual spend on IT could be used to build thousands of schools every year or to employ hundreds of thousands of nurses in the NHS.

"Today only 30%, we estimate, of our projects and programmes are successful," he told a conference. "It is not sustainable for us as a government to continue to spend at these levels. We need to up the quality of what we do at a reduced cost of doing so."

The extensive list of failed projects calls into question other major government IT programmes, such as the proposed £5bn ID cards scheme.