Imagine, if you are not lucky enough to be there today, upland Northumberland: England's last wilderness. It is called the land of the far horizon, not just because you can see for miles but because it allows the mind to wander freely. You can hear the song of the curlew, the call of the golden plover and watch the black grouse performing its mating rituals with all the swagger of the lads out clubbing in Newcastle, an hour away by road. You can walk for hours and hardly see another soul.

In 1956 much of rural, inland Northumberland was designated a National Park. At the heart of it was and still is an anomaly: Otterburn, a vast military training area. So at the same time as hearing the wind whistling across the wide open spaces that roll down to Hadrian's Wall (another military legacy), you could perhaps hear the bone-shaking blast of rockets or the dull crump of shells landing. The noise is enough to shake the plates on the dressers of people who live nearby. And the Ministry of Defence wants to build a further development to accommodate training with heavier and longer-range weapons. Ministers are deciding how to square this with a growing demand by the nation for access to beautiful, tranquil, unspoilt places.

Long before the National Parks were designated, the army used the wilder areas of Britain for its training. It came to Northumberland in 1911. Today the MoD landholding in National Parks is significant: 44,000 hectares. National Parks contain just over a quarter of the MoD's rural estate, the major training areas being in Northumberland (almost a quarter of the park), Dartmoor (15 per cent), and Pembrokeshire Coast (5 per cent, including the coastal national trail and some of the finest sea-cliff climbing anywhere in the world). In making these observations, I am not questioning the need for military training, but I am questioning the where and how of it. I am not the first person to do so.

John Dower, one of the architects of our modern-day National Park system, wrote in his 1945 report: "Few national purposes are more vital or more rich in promise of health and happiness than the provision of ... large, open and beautiful tracts of country in which holidays can be freely and inexpensively enjoyed". Of damaging practices, including "military occupation" in these areas he wrote: "It is not, of course, a question of prohibiting such uses of land anywhere and everywhere: most of them are essential to the national economy and suitable sites must be found for them. But it matters enormously where and how. In National Park areas the less of them the better". At the end of the 50th anniversary of the 1949 National Parks and Access to the Countryside Act, we should be looking at less rather than more.

There are several reasons for this. National Parks are designated for two purposes: conserving and enhancing the natural beauty, wildlife and cultural heritage and also promoting the understanding and public enjoyment of the special qualities of the National Park areas. There is an inherent conflict between the second purpose and military training, particularly live firing. You just cannot go there when the live firing is going on. In 1977 Baroness Sharp looked into the question of military training on Dartmoor and called it "discordant, incongruous and inconsistent". The government of the day agreed and also said it could not see any way out of the dilemma. In 1991 the National Parks Review Panel concluded that the live firing ranges must go from the Parks quickly, with a long-term objective of removing all military activity.

Hold on - you might say here - surely the MoD is to be praised for its conservation? It is certainly true that during the 50s and 60s, when intensive agriculture and forestry threatened the uplands, MoD ownership provided habitat and species protection - which has brought lasting benefits. But the impacts of military training today are greater. The proposed loss of 25 hectares of habitat in Northumberland to tarmac and concrete is a blow by any standards. New weapons are more polluting, noisier, more mobile and longer-range.

So what can be done? I suggest two ways forward: first, a national strategic review; and second, better management. The MoD is starting to address the latter.

The main management issue is the difference between days booked for live firing (and therefore advertised as closed to access) and days actually used. On Dartmoor, for instance, in the last 11 years, live firing has on average happened on two out of every three days when the ranges are advertised as closed. There is huge demand for access to these areas: Tavy Cleave is one of the most spectacular valleys on Dartmoor - and on a third of the days it was closed in 1997, it could have been open.

The Pembrokeshire Coast National Park has an immensely popular coastal trail which boosts the local economy. But when walkers arrive at the military ranges they have to detour inland. They can easily miss some of the best walking in Britain (even when there is no firing).

The MoD has promised to improve the booking system and its public information: introducing telephone hot lines with up-to-date information on access would make a big difference. Managing the training slots on the ranges more efficiently would also help. The MoD is drawing up integrated land management plans for its major training areas - including those in National Parks - to be finished in early 2000. National Park Authorities and others who have helped draw these up have praised the open consultation which could lead to significant long-term gains.

The MoD could also lead the field on providing open access. The dry training area north of the River Coquet in Northumberland would be perfect for open access. The MoD has even cleared the area of old munitions. There is no reason for access restrictions here any longer.

But good management and good practice do not address the "where" and "how" questions. The National Parks Review Panel and the Countryside Commission called for a "national, public strategic review of military training needs". No government has yet grasped the nettle. The MoD is now drawing up an estate strategy, which includes measures to improve its performance on the environment and access. While this is welcome, it does not meet our modern expectations of the balance between military needs and the wider context. Defence, yes, but not at the expense of what our soldiers are being asked to defend.

It's a matter of priorities. We need a defence force and they need to train, but the people of Britain also need the freedom of wide open spaces to discover the joy of wandering in wild country in a pressured, technological age.

I dream, as I look into the new millennium, of being able to walk across the wild, empty moorland of the Otterburn ranges in Northumberland or to climb spontaneously, with the minimum of briefings and permits, on the sheer limestone cliffs of Range West in Pembrokeshire with the sea crashing below me. With a little accommodation on both sides - backed by the sort of public prompting that the Independent on Sunday's "Out of Bounds" campaign provides - I'm sure both will be possible.

Sir Chris Bonington CBE is president of the Council for National Parks.