Writing in The Times, Davis describes Google as "the last company I would trust with data belonging to me," due to its poor record on privacy.
In April, party leader David Cameron floated the idea of NHS patients making use of online health record services such as Google Health or Microsoft Health Vault.
In July, The Times reported that the party was considering the two company's services for NHS records if it wins the next election. Davis writes that his heart sank when he read that, and hoped that it was the unapproved work of a young researcher.
"What was proposed was both dangerous in its own right, and hazardous to the public acceptability of necessary reforms to the state's handling of our private information," he writes.
Noting that Google's market capitalisation is £79bn, he adds: "It represents the value of exploiting its customers' private data for commercial ends." Both Google and Microsoft see their free health record services, neither of which is available in the UK, as ways to boost advertising revenues.
Davis says that companies should not be able to make money from holding health data. "Health information has to be secure, and should not be available to be used for commercial purposes. That means it should not be sold on, it should not be data mined for commercial insights, and it should not be used for targeted advertising," he writes.
He adds that patients' health data should be held on computers within the UK, ensuring it is subject to British data protection and privacy laws.
However, Davis supports the idea of companies holding the public's personal data, if people have the ability to choose where it is stored: "Ownership, control, and 'property rights' in the trail of online information that makes up our virtual identities should rest with each individual," he writes.
He adds that companies are subject to legal action and reputational damage if they lose data: "So private companies are better than the state, but they are not saints. Accordingly, before any government privatises personal data management, we should be clear about the rules and the structure."
Davis resigned last year as shadow home secretary to fight a by-election over erosions of civil liberties – despite the fact that the Conservative leadership agreed with him on many aspects of this issue, such as wanting to abolish the identity card scheme. Before that, in 2005, he ran unsuccessfully against Cameron for the party leadership.
