On World Mental Health Day 160 Members of Parliament have written to Prime Minister Theresa May demanding she ring-fence mental health spending.

The Labour politicians called on Mrs May to "make a vital change that will advance the cause of mental health".

The Prime Minister has previously made commitments to ending the "burning injustice" that saw too many people with mental health problems denied help.

In her first speech as PM outside Downing Street she identified the huge disparity between physical and mental health treatment saying: "If you suffer from mental health problems, there’s not enough help to hand."

And last week in her speech to the Tory Party Conference Mrs May said the Tories were "Investing more in mental health than ever before".

The Health and Social Care Act 2012 created a new legal responsibility for the NHS to deliver ‘parity of esteem’ between physical and mental health, which the coalition government committed to achieving by 2020.

But critics say there is little evidence that the government has put their money where their mouth is.

Since most mental health funding is not ring-fenced the concern is that cash-strapped NHS trusts use any extra funding to plug gaps elsewhere.

More than 6,000 mental health nurses and doctors have been cut from the NHS in England since 2010.

For the fourth year in a row, the government has failed to deliver on its promise to increase the money reaching frontline services.

For the second year is a row more than half of Clinical Commissioning Groups across England report that they plan to reduce the proportion of the amount they spend on mental health.

Some areas are allocating just 6% of their budgets on mental health.

Health secretary Jeremy Hunthas promised that an extra £1.3bn would be invested annually in mental health services by 2021.

But campaigners are worried that won't be enough to make up for years of cuts.

The MPs wrote: "‘We would like to see this aspiration become a reality and believe ring-fencing will get us one step closer to real equality for mental health."

"We see this injustice every day in our constituencies. Our constituents face long waits to access mental health services, if they get a referral at all.

"The number of young people and adults turning up at A&E in a crisis continues to rise.

"The amount and quality of contact provided in the community has diminished significantly. And too often inpatient treatment means leaving family and friends for a unit hundreds of miles from home."

The MPs were brought together by Luciana Berger, Labour MP for Liverpool Wavertree and President of the Labour Campaign for Mental Health.

She said that the response to the letter from colleagues had been overwhelming and heartening.

"As constituency MPs we see the reality of people with mental health problems unable to access the services they need. Talking is important but it is not enough. The government – and Mrs May who has made repeated promises – must act today," Ms Berger said.