As anyone who has ever been lucky enough to spend time in a psychiatric hospital knows, you don’t have to be completely mad to be there. A lot of us end up in the care of mental health professionals and jacked up on all sorts of crazy-person meds because something’s just not right: you know it, I know it, the dog in the street knows it. Those people are looking at us funny; those voices just won’t quieten down; it really isn’t safe out on the streets, so it must be better to draw the curtains, triple-lock the door and sit quietly in the dark eating only tinned fruit and bottled water. The old mental weather can get pretty stormy sometimes, even for the most resilient among us, but the thunder and lightning will usually pass, and for the time being at least we’ll be able to function normally again.

Daniel Freeman, God bless him, a professor of clinical psychology at Oxford, has devoted his life to the research and treatment of paranoia and persecutory delusions, which he defines as ‘an excessive mistrust of others in relation to the self’. The man’s a saint, frankly, for putting up with people like you and me, people who are convinced that all those other damn evil people are not at all to be trusted, including people like Daniel Freeman – because what does he know?

It turns out that he knows rather a lot. A professorial fellow at Magdalen College, Oxford, he is a consultant clinical psychologist, a recipient of the British Psychological Society Presidents’ Award for distinguished contributions to psychological knowledge, the author of almost a dozen books and hundreds of journal articles, and a co-founder of the Feeling Safe Programme, a cognitive-behavioural treatment for patients with psychosis, which is proven to be the most effective psychological treatment for persecutory delusions.

The old mental weather can get pretty stormy sometimes, even for the most resilient of us

Freeman estimates that between 1 and 3 per cent of the population experience severe paranoia, that another 5 to 6 per cent have occasional distressing delusions, and that an additional 10 to 15 per cent suffer from ‘regular, albeit milder, paranoid thoughts’.