Government spending is finally laid bare (all 120 gigabytes of it)

Whitehall experienced a quiet revolution yesterday as the Government opened its books for the first time. The list of every spending decision by ministers and civil servants in the past two years contained details of millions of items of expenditure covering more than £1.2trn of taxpayers' money.

There was no compromise with the public in making the material reader-friendly – or even comprehensible – as the Treasury simply released a mass of computer files holding 120 gigabytes of information. All were couched in the language of accountants impenetrable to the uninitiated. And yet the move is likely to be seen in years to come as a turning-point for Whitehall, where a culture of secrecy has been ingrained in generations of civil servants.

The torrent of information, the largest release of official information in British history, covers every element of state spending from public sector pay and pensions to the Olympics and the Civil List. It will be pored over by freedom-of-information campaigners, computer analysts and technically-minded politicians for evidence of apparent profligacy with public money.

For example, the previous government had spent more than £1.8bn on consultants in the last financial year, an increase of £300m on the previous 12 months. The biggest spenders were the Department of Health (£480m), the Department for International Development (£288m) and the Home Office (£194m). Further number-crunching suggested the former government's monthly spending shot up in March as the end of the financial year – and the general election – approached.

Such is the density and complexity of the information released that it is likely that a whole hi-tech industry will spring up to decode it. Detailed information about where the state spends its income will be invaluable for suppliers bidding to win a share of lucrative state sector contracts.

The spending details were contained in the Combined On-line Information System, known by the appropriate acronym of Coins. It is among an array of Whitehall databases that are being published as part of David Cameron's commitment to greater openness.

Previously, only headline figures for Whitehall spending were announced at the Budget. There would, for example, be only the most limited breakdown of the annual £135bn-plus spending of the Department for Work and Pensions.

The Treasury admitted that the information was "in its raw form, requiring technical expertise to process", but added: "Institutions and experts will be able to process the data as they wish and present it in a way that is more accessible to the general public." It plans to release full spending information covering the period back to 2005 and promised it would attempt in future to produce it in "a simpler, more accessible format".

Danny Alexander, the new Chief Secretary to the Treasury, said: "For too long, the previous government acted as if the public had no right to know where their hard earned taxes were spent. Today we have lifted that veil of secrecy."

The Taxpayers' Alliance campaign group hailed the publication as a "fantastic victory for openness". Its chief executive, Matthew Elliot, said: "There is an army of enthusiastic, skilled amateurs out there who will gladly explore and use this information to suggest ways in which the Government can save money and improve public services."

But Tom Scampion, information and technology risk partner for the business advisory firm Deloitte, said: "There is little point publishing information if it cannot be easily understood or has the potential to be manipulated at the expense of its original purpose."

Mr Cameron promised to rip the "cloak of secrecy" from Government to restore public confidence in the political process, beginning with the publication of the names, pay and perks of the 172 top civil servants who earn more than £150,000 and will continue with the disclosure of MRSA and Clostridium difficile rates at hospitals and detailed street-by-street crime data.

The top 20 spenders on consultants

Health 480,402

International Development 288,110

Home Office 194,116

Transport 131,985

Work and Pensions 110,827

Children, Schools and Families 94,541

Environment, Food and Rural Affairs 86,072

Ministry of Defence 79,814

HM Treasury 57,323

HM Revenue and Customs 45,230

Communities and Local Government 28,616

Northern Ireland Executive 24,263

Cabinet Office 22,370

Foreign and Commonwealth Office 21,700

Welsh Assembly Government 21,191

Office for National Statistics 18,448

HM Procurator General and Treasury Solicitor 18,241

Ministry of Justice 17,844

Department for Business Innovation and Skills 11,731

Scottish Government 8,300