Almost one in six mental health patients are attempting suicide as they face "unacceptably long" waits for help, experts have warned.
Many patients waiting for psychological therapies have also self-harmed and had suicidal thoughts, a powerful coalition of health charities, royal colleges and service providers said.
The coalition, called We Need to Talk, said that there are "huge variations" in referral rates and waiting times around the country which are leading to patients becoming more unwell.
The comments come after a poll of 2,000 people who have tried to access therapy in the last two years found that almost one in 10 were waiting over a year between referral and assessment and 41% waited more than three months.
While on waiting lists 67% said that they felt more mentally unwell and four in 10 said they have harmed themselves.
Two-thirds said they experienced suicidal thoughts and 16% said they had attempted suicide.
The organisations said that since 2007 the Improving Access to Psychological Therapies (IAPT) programme has meant that more people can access talking therapies.
They added that the Government has invested in this programme but progress has been "patchy" and more must be done to give people with mental health problems the help and support that they need.
They called on the next government to make talking therapies an "immediate priority".
"Mental health services aren't currently set up to cope with demand," said Paul Farmer, chairman of the We Need to Talk coalition and chief executive of mental health charity Mind.
"We know that in some parts of the country investment in IAPT and other models has transformed lives as people have been able to access the help they need when they need it. But far too many are facing unacceptably long waits or are struggling to even get a referral. This simply isn't good enough.
"At the same time as people are waiting for psychological therapies, prescriptions for antidepressants rise and rise and we have seen mental health services struggle to cope with the demand for beds and other crisis services.
"All three main political parties have been in power in the time we have had IAPT, so we know the commitment is there but we have yet to see the ambitions of the programme made a reality on the ground.
"Whoever forms our next government must redouble their efforts and make this a priority, ensuring fair access and establishing waiting times targets so that no matter where you live, you can get the help you need when you need it.
"We are calling on them to ensure the NHS in England offers a full range of evidence-based psychological therapies to everyone who needs them within 28 days of requesting a referral."
Care and Support Minister, Norman Lamb, said: "It is unacceptable for anyone with mental health problems to have to wait over a year for treatment.
"More people than ever before are getting talking therapies thanks to our £400 million investment. Nationally, 62% of people referred for talking therapies are treated within 28 days but we know there is more to do, which is why we're introducing access and waiting time standards for mental health from next year."
Labour's shadow public health minister Luciana Berger added: "These findings show the extent of the pressure our mental health services are under.
"It is appalling that people are waiting so long for psychological therapies their conditions are becoming much worse or they are forced to pay for private treatment to get the help that they need. The next Labour government will ensure that the right to counselling for mental illness is enshrined in the NHS constitution. We are placing mental health at the heart of our vision for whole person care to ensure that it gets the attention and focus it so desperately needs."
Dr Martin McShane, NHS England's director for long term conditions, added: "NHS England recognises the importance of talking therapies and has taken action to improve access to psychological therapies for both children and adults year on year.
"As part of our commitment to 'parity of esteem', we would like to be in a position to introduce for the first time access standards/waiting times for mental health services, on a phased basis, beginning next year."
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