Before July 2022, only GPs could give out a 'fit note', which tells employers if a patient is too ill to work, or give other recommendations, such as reducing their working hours.
But now other healthcare professionals, including doctors, nurses, occupational therapists, pharmacists and physiotherapists can certify the notes as well.
The Health Foundation said sick pay reform is needed to help people stay connected to their work when off sick, as many still want or need to work.
NHS Digital figures show 26,396 sick notes were issued to patients in the former NHS Frimley CCG area between April and June – slightly fewer than the same period last year, when 26,859 were issued.
This meant an average of 1,714 fit notes were given out for every 100,000 patients aged 18 to 65 years of the GP population in east Berkshire, north east Hampshire, Farnham and Surrey Heath.
These figures are for the number of individual fit notes, rather than patients – a single patient may have been given multiple notes over the course of the quarter.
Of those with a diagnosis disclosed, a mental health and behavioural disorder was the top reason for every former CCG area, with 2,958 in east Berkshire, north east Hampshire, Farnham and Surrey Heath.
Sarah Scobie, director of research at the Nuffield Trust, said: “More fit notes relating to mental health problems is just one way that worsening mental health has become starkly visible in recent years.
“In England, cases of depression, anxiety and psychosis have increased every year over the last five years. Against a backdrop of increasing referrals for talking therapy and community mental health care, the ability of services to meet people’s needs is diminishing.”
The highest regional rate recorded in the three months to June was in the North West, with 3,040 notes issued per 100,000 patients, while London had the lowest – 1,652.
In England, out of the 2.5 million fit notes issued this spring, more than 1.1 million (44%) were given out for five weeks or longer, which is considered a long-term sickness.
Ms Scobie added: “We have seen a worrying rise in economic inactivity in recent years due to long-term sickness, with more fit notes issued than before the pandemic.
“A sick workforce is bad news for the economy, but tackling recent rises in long-term sickness will also represent a huge challenge to health services as they grapple with the demands of post-pandemic recovery.”
Sharlene McGee, policy manager at the Health Foundation, said: “A long-term preventative approach is needed to help more people with deteriorating health from falling out of work altogether. We need better mechanisms – including sick pay reform – to help people stay connected to their work when off sick.
“The Autumn Statement is an opportunity for the Government to grasp this issue and make impactful changes. Ministers are considering changes to occupational health services to increase coverage in workplaces.
“However, these should go further, providing financial support to smaller businesses and encouraging employers to use their influence to improve health with better sickness and return-to-work management.”
The NHS figures do not cover all fit notes, as some patients may opt out from sharing data. Less than 1% of the total number of fit notes issued each month in England were duplicates.