The Government spent £4.3bn with the traditional big six IT firms last year, according to think tank Institute for Government.
Here's who they are and how much they earned.
Hewlett Packard pulled in £1.7bn in each of the last two years to become the largest single recipient of Government money, according to the report.
But a think tank spokesman warned the figures were being reexamined after the Government disputed them.
The researchers initially believed 86% of HP's public sector revenue came from a job centre contract with the Department for Work and Pensions (DWP), but the DWP told CBR the figure was "just wrong".
A spokesman added: "The correct figure is several hundred million a year to cover the majority of IT services and IT development used by DWP.
"This includes the IT platforms which are used for the processing of benefits and pensions."
The French IT services firm also counted £997m from public sector contracts in 2012, found the think tank.