Mishcon de Reya is bringing a representative action on behalf of Mr Andrew Prismall and the approximately 1.6 million individuals whose confidential medical records were obtained by Google and DeepMind Technologies in breach of data protection laws.
The claim arises out of an arrangement formed in 2015 between Google and DeepMind and the Royal Free London NHS Foundation Trust, under which the tech companies obtained approximately 1.6 million individuals' confidential medical records without their knowledge or consent.
The action is an important step in seeking to address the very real public concerns about large-scale access to, and use of, private health data by technology companies.
It also raises issues regarding the precise status and responsibility of such technology companies in the data protection context, both in this specific case, and potentially more generally.
Mr Prismall said: "Given the very positive experience of the NHS that I have always had during my various treatments, I was greatly concerned to find that a tech giant had ended up with my confidential medical records.
"As a patient having any sort of medical treatment, the last thing you would expect is your private medical records to be in the hands of one of the world's biggest technology companies.
"I hope that this case will help achieve a fair outcome and closure for all of the patients whose confidential records were obtained in this instance without their knowledge or consent."
The case is being led by Mishcon Partner Ben Lasserson, who said: "This important claim should help to answer fundamental questions about the handling of sensitive personal data and special category data.
"It comes at a time of heightened public interest and understandable concern over who has access to people's personal data and medical records and how this access is managed."