The acquisition of a 140-acre farm on the limestone headland of the Great Orme may not appear momentous, but this small Welsh treasure protected by the National Trust is the latest step in a journey that has transformed the character of our coast.

Fifty years ago, Britain’s biggest coastal landowner was the Ministry of Defence. More than five miles of pristine coastline were being lost each year – to caravan parks, oil refineries and nuclear power stations. The wild coastline that remained was usually fenced off or overgrown.

Strolling the south-west coast path, or the new 870-mile Wales coast path today, it is easy to forget the amazing efforts to prevent unspoilt cliffs and coves resembling the high-rise tourist traps of the Mediterranean or the suburban sprawl of much of the Sussex coast. Social and economic trends have helped – the decline of the domestic seaside holiday with the rise of cheap flights reduced pressure on the British seaside – but, mostly, the coast has been protected by local action and charity.

In 1965, the National Trust launched Enterprise Neptune, a fundraising campaign to save the seaside from development. It caught the popular imagination of the day – even featuring on The Archers – and has continued, quietly, to protect the coast. Supported by local residents and small donations from people who often live as far away as possible from the sea (only 70 miles, in our uniquely coastal nation), the National Trust has become Britain’s biggest coastal landowner, safeguarding more than 775 miles of the coast of England, Wales and Northern Ireland. (The National Trust for Scotland is a separate organisation.)

For all its associations with stately homes, the National Trust grew out of the Victorian movement to protect the commons of London. The seaside is now a contemporary commons – freely accessible and preserved for everyone, for ever. Many of these miles are as beautiful as might be expected – a third of the Cornish coast is owned by the Trust – but many are less celebrated: the charity helped rehabilitate Durham’s coal-wrecked coastline and has taken on badly contaminated military sites such as Orford Ness in Suffolk, allowing its cold war ruins to gently decay rather than tidying them up.

The Trust has not single-handedly saved the coast. Other charities, including the Wildlife Trusts and the RSPB have also acquired many important estuaries and marshes. Tighter planning regulations, and government-led initiatives such as national parks and areas of outstanding natural beauty have helped hugely.

But it is striking how much has been achieved by the big society, to use language calibrated to attract this government’s attention. And attracting the attention of David Cameron’s administration will be important because the coast will change perhaps more dramatically than ever in the coming century.

While the battle against intrusive coastal housing has largely been won, marine conservation is still in its infancy. Our hunger for energy will see empty horizons filled with offshore wind farms, new nuclear power stations and tidal barrages. Tidal could provide positive opportunities to reshape our coast in a way that augments wildlife and recreation but other developments will industrialise once wild landscapes.

Climate change, rising seas and increasingly fierce storms also threaten to redraw the coastline and throw at least 7,000 homes into the sea this century. Because British governments still cling to an archaic law which absolves them of ever compensating people who lose homes to the waves, this erosion could accelerate the decline of coastal communities impoverished by the loss of fishing and domestic tourism.

Open space by the sea brings health benefits, solace, artistic inspiration and exhilaration to every generation

There are no easy answers to these big questions but a simple footpath could help. In announcing its acquisition on the Great Orme, the National Trust signalled its determination to hold the government to its commitment to create a coast path for England by 2020. Conservationists fear this will become another promise broken by austerity, but the government would be foolish to abandon such a popular policy. A coast path is a far more inspiring piece of infrastructure than HS2, with real economic heft: the south-west coast path generates £436m for the regional economy each year, supporting 10,000 jobs.

A pathway around England is far more than an economic prop, however. The Trust’s former director-general, Fiona Reynolds, recently argued that it could be the first step in the creation of a new coastal zone, a kind of decentralised national park in which local people have a real say in how their coast is developed and cared for. As well as a footpath, a government with real vision could create a coastal national park which harnessed the economic regeneration of impoverished areas with environmental protection, recreation and a sensible discussion of how best to adapt to rising seas.

I can’t think of many finer legacies for any politician. Perhaps the National Trust could be more radical too, and use Neptune funds to preserve more unusual coastal treasures – how about preserving a pier or some of the unique, threatened plotlands coast such as Jaywick Sands?

Open space by the sea brings immeasurable health benefits, solace, artistic inspiration and exhilaration to every generation. We must summon every piece of our passion for the coast in the coming century to maintain this rich resource for everybody.