HMRC has spent over £3.7bn with integrator Capgemini over the past five years for its work under the Aspire contract.
Capgemini is the lead supplier under the Aspire deal, in which around 300 subcontractors - including Fujitsu and BT - are involved. Capgemini pays 65 per cent of its fees on to its subcontractors, keeping 35 per cent - or just over £1.2bn in this case - for itself.
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HMRC revealed that the fees paid per year break down as follows:
2008/09: £777.1m 2009/10: £728.9m 2010/11: £757.8m 2011/12: £735.5m 2012/13: £773.5m
This shows that the current financial year has seen the largest payment so far under the deal - at a time when the government has pledged to reduce large public sector contracts, and move to smaller, more agile deals with SMEs.
This is part of the Open Standards Principles announced by Cabinet Office Minister Francis Maude in June, which states a target of a quarter of all government procurement should involved SMEs by 2015.
It also comes after HMRC revealed plans earlier this year to double the number of its in-house software developers in order to reduce the need for expensive outsourced expertise from firms like Capgemini.
The tax authority refused to reveal a more detailed breakdown of its costs, citing commercial sensitivity.
"It is considered that disclosure of details about cost breakdown of payments made by HMRC to Capgemini would prejudice the commercial interests of HMRC as a contracting authority and our ability to deliver best value.
"It is also considered that release of such information would weaken our supplier's position in a competitive environment by revealing market-sensitive information or information of potential usefulness to its competitors."
The Aspire contract, originally signed between Capgemini and HMRC in 2004, covers the provision of the government department's IT requirement, including desktops, networks and data centres.
Originally worth £2.8bn and due to run for 10 years, the deal was revised and extended in 2009, and will now expire in 2017.
And last year the deal was revised again, with £200m shaved off its costs over the contract duration. However, with overall costs at an all-time high this year, and with details sparse on what exactly the taxpayer gets for these sums, it is hard to judge whether this represents value for money.