The Mental Welfare Commission for Scotland, which produced the report, said the Covid-19 pandemic had exacerbated existing problems with the law, while Liberal Democrat MSP Alex Cole-Hamilton warned people’s rights had been breached.
Mental health detentions increased 9 per cent from March 2020 to February this year, above the average year-on-year rise of 5 per cent in the previous five years.
For the first time, fewer than half of detentions met the safeguarding standard of involving a mental health officer. This fell from 52 per cent the previous year to 44 per cent.
There were 147 deaths among people detained, including 19 due to Covid-19.
This is an increase from an average of 110 a year in the past five years, but the commission notes the reporting system has also been improved.
A total of 10,059 detentions were recorded in this period, compared to 9,222 the year before. The most significant increases were seen in larger health boards.
Dr Arun Chopra, medical director at the Mental Welfare Commission, said the organisation was “concerned” about the increase in detentions.
The reason for this is unknown, he said, but may be related to the pandemic.
Dr Chopra said: “In checking for a potential link with the pandemic, we looked at whether there were more people detained in an emergency last year who did not have a history of detention in the past, but we found that the proportion of people who had or did not have previous episodes were the same last year, as in previous years.
"We can say that the pandemic exacerbated existing problems with the law. We are some years away from any new legislation that may follow recommendations from the independent review into Scottish Mental Health Law.
"In the meantime, best practice is not being realised and we will continue to raise our concerns over the lack of mental health officer consent to detentions.
Mr Cole-Hamilton said: “Peoples' rights have been breached year after year because of the scandalous under-provision of every type of mental health staff.
"It’s small wonder that the UN Committee on the Rights with People with disabilities should repeatedly upbraid Scotland on the government’s record here.
"The detention of thousands of Scots without the consent of specialist mental health staff shines a spotlight on how this country has let down some of our most vulnerable citizens.”
An investigation published last month by The Ferret found people had faced “unacceptable” delays of more than three years before leaving mental health wards, despite being well enough to be discharged.
Data released under Freedom of Information legislation from Scotland’s 14 health boards had shown thousands of instances of delay over the past three years in people leaving psychiatric hospitals.
The commission said it was “not acceptable” for people to spend years in hospital awaiting discharge in the wake of figures being released.
The Scottish Government has been contacted for comment.