Managing a national park is challenging. It needs the right balance between conservation and recreation. National park authorities need to conserve wildlife and habitats, but also encourage people to enjoy and learn from the countryside. This can cause conflicts.
To help national park authorities make decisions between conservation and recreation, the National Parks Policy Review Committee made a recommendation in 1974, which is now known as the 'Sandford Principle', named after Lord Sandford who was chair of the committee.
This principle was updated in the 1995 Environment Act, to say;
"If it appears that there is a conflict between those purposes, [the National Park Authority] shall attach greater weight to the purpose of conserving and enhancing the natural beauty, wildlife and cultural heritage of the area"
In other words: If there is a conflict between protecting the environment and people enjoying the environment, that can't be resolved by management, then protecting the environment is more important.
A fisherman would like to fish at a lake shore. He has access to the lake, so he can enjoy his day fishing, which fulfils the national park purpose of understanding and enjoyment.
There are also ospreys nesting in a tree nearby, which catch fish in the lake. Ospreys are a protected bird species and are easily disturbed by noises and movements during their breeding season. Looking after the breeding osprey fulfils the national park purpose of conservation.
In this example the two main purposes of national parks -- conservation, and understanding and enjoyment -- are in conflict. By applying the Sandford Principle the conflict is resolved and conservation, in this case the nesting ospreys, take priority. The fisherman is encouraged to find another fishing spot during the osprey breeding season. When the ospreys have migrated away in winter, the fisherman can fish in the lake.