"It has been considered acceptable that most people [with psychiatric problems] don't receive treatment," he says. "It is part of the stigma. We in psychiatry almost take it for granted that our patients, our hospitals and ourselves will be treated as second-class citizens. People are pushing for improved targets in cancer treatment and complain when they are not met - yet they are way beyond what we could possibly achieve."
It is two years since parity was first mentioned in the NHS Mandate, the contract between the Government and NHS England setting out the service's ambitions. Last month, Simon Stevens, the chief executive of NHS England, cemented the ambition by setting a target for "genuine parity of esteem between physical and mental health" to be achieved by 2020, with new waiting standards and extra investment in care for young people promised next year.
There is, however, a mountain to climb. People with severe mental illness die 15 to 20 years earlier than those without it - one of the greatest of all health inequalities. Mental illness is the single largest cause of disability in the UK, costing the economy 100 billion pounds a year (equivalent to the entire cost of the NHS). It accounts for a quarter of the total burden of disease but consumes just 13 per cent of the resources.
The deal that people with mental illness get is, in a word, unfair. Wessely does not use the word, yet it was his concern for patients getting an unfair deal that drew him to the two groups on which he has built his career: people with chronic fatigue, and soldiers with Gulf War syndrome. In both cases, these were patients whose needs had been neglected by mainstream medicine but who, by dint of careful study, he was eventually able to help. Now, he wants to focus on all those suffering with mental illness who, because of discrimination, are also without help.
Aged 58, he is an optimist, full of enthusiasm, which makes him unusual among doctors of his vintage. He could have been a historian or a journalist, he says, but having chosen medicine, there was never any doubt that he would end up doing psychiatry. It had the most interesting arguments.
"Tumour biologists can get excited about a new classification of cytokines but no one else is interested. The issues we debate are issues on which everyone has a view. When does sadness become depression? When does shyness become social phobia? When does a bookish kid, as I was, become Asperger's? You have to be dull if you get bored by these."
He regularly cycles to work at the swish new Royal College of Psychiatrists premises in east London, and, on the day we meet, apologises to his press officer that he is without a tie for the photographer, before begging her to fetch him a sandwich for lunch. He has no interest in the trappings of office. Raised in Sheffield, his mother, a Methodist, was a musician and his father, a Jewish emigre from Czechoslovakia, was a teacher and he assumed that "public service was what you did".
To underline the intellectual credentials of his discipline, Wessely reels off the list of issues that have crossed his presidential desk in the past week - assisted dying, the Winterbourne View scandal, capacity and the Mental Health Act, the role of coercion and "DSM wars" (a dispute over what conditions should be included in the psychiatrist's bible). It is perhaps a reflection of psychiatry's wars that I cannot imagine the president of any other medical college presenting a similar list.
The most urgent task is to preserve a mental health service that is threatened by the continuing squeeze on NHS funds, notwithstanding the announcement of an extra 1.3 billion pounds in the Chancellor's Autumn Statement.
Mental health services have been savagely cut, Wessely says, as NHS Trusts have struggled to balance their books. "If you run frontline mental-health care, you are in serious trouble, losing staff and resources," he says. "The problem for all the parties is that they have no proposals to reverse the decline."
His focus is on primary care, where most mental health care is delivered. "If primary care collapses, we are doomed," he says. "My vision is that we come much closer to primary care than in the past. Most doctors have a major psychological problem with moving away from hospital. It is impossible for surgeons and difficult for physicians. We [mental health services] are the only people who trigger celebrations when we close a hospital and protests when we open one. I would like to see us working much closer to GPs."
He has plenty to prove over the next two years, not least to the GP with whom he lives.He is married to Clare Gerada, the outspoken former president of the Royal College of GPs, who waged an effective but ultimately unsuccessful campaign against the Health and Social Care Act, which Wessely says is now causing mayhem in the NHS, as she predicted. Though more cautious than his wife, he is more media-savvy than most Royal Medical College presidents, with an eye for a quote. At the couple's 25th wedding anniversary last year, their sons caused laughter when they summed up their parents' relationship in a single word: "competitive."
His competitiveness has got him into trouble in the past. His findings on chronic fatigue and Gulf War syndrome proved controversial because activists in both groups claimed that their symptoms had a biological cause - a virus in the case of chronic fatigue and vaccines, depleted uranium or smoke from oil fires in the case of Gulf War syndrome. Wessely argued that whatever the cause - which could not be determined in either condition - it was the treatment that mattered. Even if a virus was the original trigger of a patient's fatigue, the challenge was how to tackle it.
"If you have been knocked over by a car in a hit-and-run accident, learning its number plate won't help you," he says.
He was first drawn to the problem as a young doctor in the late 1980s working at the National Hospital for Neurology and Neurosurgery in Queen's Square, London, when he encountered patients with what was then thought to be a strange muscle disease. "It was an interesting problem and they were interesting people. They were very disabled and no one was doing anything for them. They were told in the media [which had dubbed the condition "yuppie flu"] that rest was best, which seemed to us a counsel of despair. We developed a new treatment and we think we did better."
He was able to demonstrate that the pattern of fatigue was not that of a neuromuscular disease, publishing his findings in what he still regards as among the most influential of his 700 research papers. The treatment he devised is a combination of cognitive behaviour therapy and "graded activity" - a step-by-step programme to get sufferers moving again. It is now standard therapy.
Not that he got much thanks. He became a hate figure in the chronic-fatigue community, which accused him of claiming that the condition was all in the mind, although he never had. But he admitted in an interview once that he "could have been more diplomatic".
He says: "I wasn't thinking about the language I used or its impact. I was just keen to get into print." He is more temperate now, but still draws the ire of some groups and has police protection of the kind provided to scientists doing experimental work with animals.
He switched focus in the mid-1990s after seeing reports of soldiers who had returned from the 1991 Gulf War with symptoms exactly like those of his chronic-fatigue patients. They were another group that was being badly served, in this case by the Ministry of Defence. It was obvious that a study comparing their experience with soldiers who had served elsewhere was needed, but the MoD turned him down. So he went to the Pentagon, which granted it. "I remember Nicholas Soames [then junior defence minister] saying he couldn't countenance research because it just made things worse," Wessely says.
The Gulf War veterans turned out to have twice as many symptoms as those who went to Bosnia. At first, Wessely and his co-authors thought that the anthrax vaccine was the cause, given to soldiers in the Gulf threatened by Saddam Hussein's chemical weapons, but not to those in Bosnia. The 2003 Iraq war put paid to that theory, leaving social and psychological factors as the likeliest explanation. The strongest factor associated with the belief that they had Gulf War syndrome, it turned out, was knowing someone else who had it.
Although many campaigners disliked this conclusion, it achieved what they had sought - Gulf War illness was recognised as a real condition and sufferers were therefore eligible for war pensions.
There was a reward, too, for Wessely. He was knighted in 2013 for services to military healthcare - one of fewer than half a dozen psychiatrists to hold the honour. If he can increase that number - physicians and surgeons hold many more - that, too, would be a blow for parity.
- The Independent