The Scottish Parliament passed the National Parks (Scotland) Act on July 5, 2000, half a century after national parks were introduced in England and Wales in 1949.

Decades of opposition by landed interests had blocked moves to establish them north of the Border so Scotland's newly-elected MSPs were keen to correct this anomaly early on.

The whole point of having national parks is to enable such areas to be managed for the benefit of the public. That requires public authorities acting on our behalf. In most other countries in the world it also involves public ownership of the land in the park – something Scotland could have pursued and should still pursue actively.

Obviously there are legitimate private interests in Scotland's national parks, but the role given to the private sector must not compromise the fundamental public purpose of the park. The balance needs to be carefully managed.

Last week, I visited the Cairngorms and was astonished at the prominent role given to large private estates in promoting and managing the area. I didn't go to visit a private estate. I didn't even go to visit the national park. I went to enjoy the hills that have been there since the ice retreated 10,000 years ago.

Scotland's national parks are in fact already subservient to some powerful private interests. This is why the comments of Fiona Logan raise concern. A national park that requires no public funding might be a laudable ambition but there is a danger that, in the process, the public interest becomes compromised by the need to generate funds from private interests which begin to drive the national park agenda.

It's not hard to imagine a situation where a national park is short of cash. Suddenly there appears a private-sector proposal for a tourism development that would solve the financial problems but be inconsistent with the aims of the park.

Scotland's national parks are currently funded by public money, voted for by the Scottish Parliament, which enables them to carry out their functions and have financial autonomy. They could easily raise more of their own running costs, not through surrendering any initiative or powers to the private sector, but by acting more as a public authority.

For example, the park authority could be given powers to raise bonds and undertake high-quality infrastructure and other capital investments on its own account. There is no reason why tourism developments need be left to the private sector and good reasons why they shouldn't.

But perhaps the biggest potential source of sustainable finance arises from the very public investment that Fiona Logan is so worried might not be forthcoming in the longer term. National parks, by definition, are some of the finest landscapes in the country and the £100 million or so of public money that has been spent in them so far has been designed to further enhance these outstanding qualities. One of the main beneficiaries of this public largesse are homeowners and landowners in the park. Some land in the park is even owned by companies in offshore tax havens.

A study of English and Welsh national parks last year found that house prices there are, on average, 45% higher than the county average. Since the public pays to enhance the environment within the park and grants planning permission (which directly and significantly increases land values), a sustainable source of future finance for Loch Lomond and the Cairngorms would be to capture some of this through a levy. I haven't done the sums but someone should – the results might be quite revealing.

It is all very well to encourage the private sector but Scotland's national parks were created by the public for the public. They should not only continue to serve the public interest, but the national park authorities should invest on our behalf and ensure our taxes are not being used to enrich land and property owners at the expense of the public purse.

Andy Wightman is a writer and researcher on land rights and the author of The Poor Had No Lawyers