The sharing of patient data is "vital" to research into life-changing illnesses including cancer, diabetes and long Covid, and has been pivotal in developing responses to the coronavirus pandemic, according to NHS Digital.
But its figures show 26,216 people in Sheffield had signed up to the national data opt-out scheme by September 1.
A stark rise in sign-ups to the existing NHS data opt-out scheme came after campaigners and groups, including the Royal College of General Practitioners, expressed concern over proposals to introduce a new data collection process in England.
The opt-out scheme allows patients to prevent confidential information held by NHS Digital from being used for purposes other than their care and treatment. This could include sharing data with analysts, clinicians and commissioners in health and social care in England.
It is different from another 'type 1' opt-out scheme, which prevents NHS Digital from collecting information from GP records, for which figures are not available.
However a campaign to make patients aware of how they could opt out of sharing GP records also gave advice on how to prevent non-GP medical records being shared too, so it is possible patients chose to do both after they were warned about the Government plans.
And the number could even be higher than 26,216, as some patients may have just chosen to opt out of sharing GP records.
Sheffield doctor Heather Sowden was one of those encouraging patients to be aware of how their medical records are being used by the Government.
Speaking to The Star in June, after the Government published its plans for NHS Digital to access records, she said: "I can’t emphasise enough how important it is for the public to have a say about what is done with their confidential medical records.
"The principles of trust, informed consent and confidentiality are at the core of the doctor-patient relationship and in this circumstance the public have neither been informed nor given their consent.”
Patient data can be used for life-saving research and, throughout the pandemic, has been used to develop the shielded patient list, to identify which treatments would be most effective for Covid-19 patients and to support the urgent commissioning of services to help people with 'long Covid', the NHS said.
In Sheffield there has been a steep rise in the number of patients choosing not to share their data via the national opt-out scheme in recent months.
NHS Digital figures show 15,602 patients in the area signed up to the scheme, which first launched in 2018, between May and September this year alone – 60 per cent of the total.
They were among more than a million people to do so across England over the same period, meaning more than three million patients have now opted out.
The Government first published details of the plan on May 12 – the morning after the Queen’s Speech, in which none of the detail was mentioned.
Medical professionals criticised ministers for the lack of public engagement around the plan, the fact that many patients were not aware that their data would be shared, and the complexity of the opt-out process.