A leaked report by a government taskforce has painted a devastating picture of England’s mental health services, revealing that the number of people killing themselves is soaring, that three-quarters of those with psychiatric conditions are not being helped, and that sick children are being sent “almost anywhere in the country” for treatment.

Details of the damning assessment have come to light just as the prime minister is planning to herald a transformation of mental health services.

The report, due to be published on Monday to coincide with an announcement by the prime minister on funding and new initiatives, lays bare a system that is routinely failing people from every walk of life.

While the prime minister is expected to trumpet his focus on mental health – six years after he pledged to put mental wellbeing at the centre of his government – his own taskforce condemns years of underinvestment and lays a significant portion of the blame on the current administration.

The study, overseen by Paul Farmer, chief executive of the mental health charity Mind, makes clear that the situation is dire despite promises of reform. “Many people struggle to get the right help at the right time, and evidence-based care is underfunded,” the draft report says. “The human cost is unacceptable and the financial cost is unaffordable.”

The taskforce’s study, A Five Year Forward View for Mental Health, publication of which was delayed for months by ministers, adds that controversial changes introduced in 2012 to the health service may even have made things worse by complicating the way treatment is delivered. It reveals:

• Suicide in England is now rising “following many years of decline”, with 4,477 people killing themselves in an average year.

• There has been a 10% increase in the number of people sectioned under the Mental Health Act over the past year, suggesting the needs of the sick are not being met early enough.

• In some parts of the country, more than 10% of children seeking help are having appointments with specialists cancelled as a result of staff shortages, yet one in 10 children and young people have a diagnosable mental health problem.

• A quarter of people with severe mental health problems need more support than is currently on offer and many are at serious risk of self-neglect.

• Despite the known impact of untreated postnatal mental health problems, less than 15% of areas provide effective services for women and 40% provide no service at all. One in five women develop a mental health problem during the perinatal period.

• Figures from 2013-14 show that the average waiting time for a child seeking a routine appointment with a mental health practitioner was 21 weeks, up from 15 weeks the year before.

• The average maximum wait for a community mental health team appointment is 30 weeks and mental health wards are far busier than guidelines allow.

The report says ministers need to find an extra £1.2bn a year for mental health services by 2020. One in four adults experience at least one diagnosable mental health problem in any given year.

In January, the prime minister announced that £290m extra would be spent up to 2020 on mental health, in particular for psychological problems related to childbirth.

It has yet to be seen if the government will fulfil all the demands made by the taskforce or ring-fence further cash announcements. In December, the Observer revealed that because of a lack of out-of-hours care, the number of children arriving at A&E departments with psychiatric conditions had risen to nearly 20,000 a year in 2014-15 – more than double the number four years ago.

The taskforce further suggests that an investment of £10m a year in services for those who are suicidal would save the lives of 400 people a year.

It also concludes that the physical needs of those with mental health issues are also ignored. It suggests a 15% reduction in smoking should be achieved by 2020 by offering targeted support for smokers and ensuring all mental health inpatient units are smoke-free by 2018.

And there should be investment in training for teachers and those involved in professional childcare to ensure that mental health problems are picked up early.

A warning about the level of service given to black African and Caribbean men is also made in the report. It says that people in this group are on average detained five times longer in secure care than other groups and more targeted care is required.

An NHS England spokesman said the leaked document was not a final version of the report.

In the UK, the Samaritans can be contacted on 116 123. In Australia, the crisis support service Lifeline is on 13 11 14. In the US, the National Suicide Prevention Hotline is 1-800-273-8255. Hotlines in other countries can be found here