We cannot afford to let mental health get drowned out by Brexit

As she entered Number 10, Theresa May announced herself as a social reformer committed to tackling the inequalities and injustices that persist in Britain.

This was a welcome statement of intent, albeit one that will be overshadowed by the Brexit negotiations and economic instability that look set to dominate the early part of her premiership.

Keeping unfashionable social issues high on the political agenda will be tough, and the record of the previous Conservative governments hardly inspires confidence. But if she really hopes to secure a legacy as a bold reformer and a champion for those left on the margins of society, May must succeed where her predecessor fell short by showing the drive and ambition to act on her promising early rhetoric around mental health.

The challenge was succinctly put on the steps of Downing Street: "If you suffer from mental health problems, there's not enough help to hand."

Mental health has always been the 'Cinderella service' in the NHS, accounting for around 13% of NHS funding despite making up a quarter of the burden of illness. People with mental ill health do not enjoy the same rights of access to evidence-based treatment, close to home and on a timely basis, as those with physical conditions. All too often they are denied the treatment they need, or are shunted across the country in search of a hospital bed during a crisis.

The Liberal Democrats spearheaded a genuine momentum for change in the Coalition Government. One of my proudest moments as a minister was launching a new five-year blueprint for transforming mental health services for children and young people, backed by £1.25bn in funding.

We delivered a historic agreement on transforming mental health crisis care. And critically, we introduced the first ever access rights and maximum waiting time standards in mental health, guaranteeing fast access to effective treatment for people with common mental health conditions and psychosis.

The mission to achieve genuine equality for mental health was taking shape, and David Cameron's majority Conservative Government had a solid platform to build on. But he depressingly failed to continue this progress - and indeed, the momentum has stalled more dramatically than most of us anticipated.

Promised investment in children's mental health care failed to materialise in the scale promised. The scandal of sending people long distances from home to receive treatment is as widespread as ever. In February, the Mental Health Taskforce delivered a landmark strategy for ending the historic discrimination against people with mental health in the NHS; five months on, the Government has still not set out how it intends to ensure that this vision becomes reality.

Most outrageous of all, there is evidence of a failure to properly implement the flagship new access standards in mental health which came into force in April. In contrast, performance against key targets in the physical health system continues to be examined in forensic detail every week in the Department of Health.

Britain needs a Prime Minister who will place mental health at the heart of their agenda. For all his hollow rhetoric, mental health was never anything more than an afterthought for Cameron; and so my challenge to Theresa May is to seize the initiative and make this a key priority for her government.

We cannot afford to let mental health get drowned out by Brexit and the wider chaos that has engulfed our political system. If the moral case for action is not compelling enough, then the estimated £105bn annual economic cost of mental illness will surely be a test of the pragmatism so often celebrated by May's colleagues.

Her maiden comments as PM hit the right note as she identified poor mental health care as a leading social malaise. While it remains to be seen whether she lives up to the weight of expectation that will now follow, some have already suggested that she will pursue her priorities with greater resolve than her predecessor - giving pride of place to policy rather than PR, substance over style. It's the sort of gritty determination that the mental health community could welcome after a year of inertia from Whitehall.

May has a historic opportunity to be remembered as the Prime Minister who made a profound difference to the lives of the one in four people who will suffer from a mental illness. Let's hope she doesn't squander it.