There's CSC, who were paid £10 billion for a failed NHS IT project [2] - and Accenture and Fujitsu who made billions from the failed 'NHS Connecting For Health' project [3]
There's HP Enterprise, IBM, Accenture and BT who have so far made £12 billion on the Universal Credit IT system which was supposed to cost £2 billion. And it's still beset by problems, of course. [4]
Obviously, there's a complex set of problems and incentives at work here. For one thing, these contractors are often paid by the hour - so they make more money if a project is late or unreliable. For another, there aren't any companies big enough they could offer a fixed-price contract without going bankrupt. For another, the government generally can't provide a specification that's succinct, clear and watertight because things like benefit systems are so complex, figuring out the requirements is 70% of the work on such a project. For another, most other sectors can lock out customers who are expensive to serve - good luck using Amazon if you're illiterate, or don't have a bank account, or don't have an address - whereas state health and benefit projects can't.
[1] https://www.theguardian.com/uk-news/2014/aug/18/uk-bill-ebor... [2] https://www.theguardian.com/society/2013/sep/18/nhs-records-... [3] https://www.bbc.co.uk/news/uk-politics-24130684 [4] https://en.wikipedia.org/wiki/Universal_Credit#cite_ref-guar...