Once upon a time, David Cameron said that general wellbeing matters as much GDP. What's it all for if a country grows richer but its people feel no better? A genuine attempt at prioritising wellbeing would be revolutionary, because the happiest people live in more equal societies, are less ridden by anxiety, enjoy good employment, are well housed and more trusting. Yet in Britain all those fundamentals indices of wellbeing are in retreat.

If aiming for happiness is beyond this government, minimising extreme pain could be within reach, if it began by prioritising scarce NHS resources entirely according to suffering. If pain was measured in a Benthamite way – the relief of the greatest suffering for the greatest number of patients – mental illness would trump most other conditions. One sufferer describes getting his broken leg slammed in a door as less excruciating than the agony caused by his depression. Yet an ingrowing toenail gets treated within a mandatory 18 weeks, while there is no waiting limit at all for treating mental illness. More than half of those referred by GPs never get any treatment, and of those who do, some wait for over a year in the deepest despair. It's even more shocking that so often children get no help.

Professors Richard Layard, an economist, and David Clark, a clinical psychologist, ratchet up their campaign for better mental treatment with their new book, Thrive. These champions of cognitive behavioural therapy have done more to turn mental health into practical politics than anyone before, though progress is slow. Their skill has been to produce evidence that a course of CBT, costing £650, can permanently rescue half of those who take the course from disabling mental illnesses. For politicians, their evidence shows that a highly systemised treatment with specifically trained therapists saves lives and money. Nice guidelines say everyone with depression and anxiety should referred for CBT – but that's not binding, so most are not. The mechanised approach invites criticism, but this strictly evidence-based therapy has the best chance of gaining political traction.

The coalition promised that mental health would get "parity of esteem" with physical health, but so far there is little sign of it. Instead the government has just cut the tariff paid for mental healthcare by more than it cut the tariff for physical treatments. Norman Lamb spoke at the launch of the Layard and Clark campaign in the Commons, protesting that mental health "was first to be cut and isn't getting a fair share of attention". Had he forgotten that he is himself a health minister who could say no?

On some other planet, Nick Clegg made an eye-catching announcement in December that all mental patients could choose where they go for treatment – NHS or private – but most wait for anything, anywhere, and many get nothing. A shortage of beds means in-patients are now often sent hundreds of miles from home, certainly not by choice. NHS England's website claims "parity of esteem" but only promises that 15% will get CBT by 2015.

As it is, cancer and heart disease rule the roost, surgeons are king and psychiatry is low in the pecking order. Politicians are not entirely to blame; they know that mental and community services, where 90% of patients are treated, should get priority, but NHS politics is governed by front-page demands for every new drug, and for intensive care to prolong the miserable last six months of life. Oppositions protest at rising waiting lists or ambulance waiting times. Jeremy Hunt doesn't call community mental services to ask who they're neglecting, he calls A&E to bellow at them for overstepping a four-hour wait. Can mental health be made as politically sensitive?

Neglect of the mentally ill is bad enough, but now consider how the Department for Work and Pensions deliberately torments them. I just met a jobcentre manager. It had to be in secret, in a Midlands hotel, several train stops away from where she works. She told me how the sick are treated and what harsh targets she is under to push them off benefits. A high proportion on employment and support allowance have mental illnesses or learning difficulties. The department denies there are targets, but she showed me a printed sheet of what are called "spinning plates", red for missed, green for hit. They just missed their 50.5% target for "off flows", getting people off ESA. They have been told to "disrupt and upset" them – in other words, bullying. That's officially described, in Orwellian fashion, as "offering further support". As all ESA claimants approach the target deadline of 65 weeks on benefits – advisers are told to report them all to the fraud department for maximum pressure. In this manager's area 16% are "sanctioned" or cut off benefits.

Of course it's not written down anywhere, but it's in the development plans of individual advisers or "work coaches". Managers repeatedly question them on why more people haven't been sanctioned. Letters are sent to the vulnerable who don't legally have to come in, but in such ambiguous wording that they look like an order to attend. Tricks are played: those ending their contributory entitlement to a year on ESA need to fill in a form for income-based ESA. But jobcentres are forbidden to stock those forms. These ill people's benefits are suddenly stopped without explanation: if they call, they're told to collect a form from the jobcentre, which doesn't stock them either. If someone calls to query an appointment they are told they will be sanctioned if they don't turn up, whatever. She said: "The DWP's hope is they won't pursue the claim."

Good advisers genuinely try to help the mentally ill left marooned on sickness benefit for years. The manager spoke of a woman with acute agoraphobia who hadn't left home for 20 years: "With tiny steps, we were getting her out, helping her see how her life could be better – a long process." But here's another perversity: if someone passes the 65-week deadline, they are abandoned. All further help is a dead loss to "spinning plates" success rates. That woman was sent back to her life of isolation: she certainly wasn't referred for CBT. For all this bullying, the work programme finds few jobs for those on ESA.

Failing to treat the mentally ill is bad enough, but this is maltreatment. There has been much outrage about lack of kindness and care in hospitals. Neglect of mental patients is every bit as bad, but deliberate cruelty by the DWP defies any concern for the wellbeing for the most vulnerable, let alone "parity of esteem".