"Chronically under-reported" was the phrase used by the poet Benjamin Zephaniah when he guest-edited BBC Radio 4's Today programme at the start of the week. He was talking about the phenomenon of the number of people who die in police custody. It was hard to disagree, when a reporter disclosed that 953 people have died in this way in England and Wales since 1990.

It was such a shocking figure that I went online to check. It turns out that it may be a conservative figure. The Independent Advisory Panel on Deaths in Custody has suggested that 5998 deaths were recorded from 2000 to 2010. There is some controversy about its figure - and to what extent these people died because of the physical-restraint methods used by the police. But this is clearly an issue of such magnitude that it is surprising that we hear so little about it.

One explanation could be that many of those who die have mental-health problems. Today suggested that almost half of those who died in this way last year were in this category; the independent panel suggests that the proportion is as high as 92 per cent. Either way, mental health is one of the areas that the modern media fastidiously ignore, which is why it took an outsider such as a poet to place it so high on the news agenda.

Many media outlets now go in for occasional guest-editors: it is a welcome development. They bring a different perspective. The picture of the world portrayed by the media is much more peculiar than is generally appreciated. Most of us accept that world-view uncritically, except on those few occasions when journalists write about something that touches us personally. Then we realise how far their truth is from ours.

But news is a shifting landscape anyway. One of the Today presenters, Evan Davies, tweeted over Christmas that he was grateful for another of the programme's guest-editors because, without this input, there was only enough real news to fill about 15 per cent of the show's three-hour slot. When there are not big events, smaller ones must be pressed in to fill the space. You might have wondered why there seem to be more people killed on the roads at Christmas, according to the bulletins. But the personal tragedy of people's dying on the roads, sadly, occurs all the year round, without making it into the news. It is just that when there is no other news, these accidents are elevated in status.

In an odd way, though, the news-dearth is a positive thing. My own newspaper has been running a Christmas appeal for Unicef's work in rescuing child soldiers from militias in the Central African Republic. Stories about continuing situations rather than events do not usually get much space; yet they often tell of a deeper and more disturbing reality than do the drama of mere events.

Thought for the Day is a little oasis that often performs this necessary function in the daily news-round. On Mr Zephaniah's day as Today editor, the Quaker Helen Drewery reflected on two incidents of horrific violence which shocked us all: the organist killed in Sheffield on his way to midnight mass, and the medical student in Delhi who died after being beaten and raped on a bus. But she used these as a jumping-off point for telling two contrasting stories of ordinary people whose actions for peace have brought extraordinary results.

Wars that have been prevented have no names, she concluded. Sometimes, it is what the news omits which should concern us most, for both good and ill.

Paul Vallely is associate editor of The Independent. Its appeal to help child soldiers is at: www.unicef.org.uk/independent, phone 0800 037 9797.