The IUCN state a national park to be a relatively large area with the following defining characteristics:
One or several ecosystems not materially altered by human exploitation and occupation, where plant and animal species, geomorphological sites and habitats are of special scientific, educational, and recreational interest or which contain a natural landscape of great beauty;
Highest competent authority of the country has taken steps to prevent or eliminate exploitation or occupation as soon as possible in the whole area and to effectively enforce the respect of ecological, geomorphological, or aesthetic features which have led to its establishment; and
Visitors are allowed to enter, under special conditions, for inspirational, educative, cultural, and recreative purposes.
Minimum size of 1,000 hectares within zones in which protection of nature takes precedence
Statutory legal protection
Budget and staff sufficient to provide sufficient effective protection
Prohibition of exploitation of natural resources (including the development of dams) qualified by such activities as sport, hunting, fishing, the need for management, facilities, etc
In America they have Yellowstone and Yosemite, Canada has the Rocky Mountains and Banff, the Democratic Republic of Congo has Virunga, South Africa has Kruger and even Poland has some 'proper' National Parks, including Magurski where I take people every year to see what 'biodiversity' really means.
In the UK we have the Lake District, which is about as far from the IUCN definition as it's possible to get; an area of over-grazed hills and plantation forestry around some lakes.
We have the Peak District which seems to be predominantly grazed pasture and some heather moorland, i.e. farmland.
We have the New Forest, which we visited last spring and were shocked to see it more over-grazed than the surrounding landscape, with woodland grazed flat and with a browse line on the trees at cattle/pony height.
We have Dartmoor, which I've only visited once but have no desire to visit again. A bleak landscape with few trees due to over-grazing.
There are some National Parks in the UK where it's possible to find some natural or semi-natural habitats, such as the Cairngorms, but even here there are many areas that are over-grazed and tree-less.
Snowdonia, our local National Park, is also vast areas of over-grazed and tree-less landscape with little wildlife to be seen, interspersed with blocks of dark forestry plantation.
Sure, there are a few birds of prey in the sky, mostly buzzards with the odd red kite, sparrowhawk, peregrine or goshawk, but the largest mammal you'll see in North Wales is the non-native fallow deer and that's very localised.
Badgers, foxes and pine martens where lynx and wolf should also be, with otters on the rivers where we should also have beavers - there are a handful, but they're isolated 'trials'.
I'm certainly not suggesting we should reintroduce wolves, or even lynx (though they'd probably fit in quite happily), but beavers are a must as a way to easily solve several problems.
They will create rich habitats for other species, increasing populations of fish and other wildlife, while holding back rainwater and helping to prevent floods.
Their dams and pools filter the water, holding back silt and farmland contaminants.
If we were to reintroduce beavers throughout the country, together with severely reducing grazing and encouraging 'marginal' habitats where wildlife can live and feed, we'd see a massive increase in our wildlife.
Of course, a massive increase from not very many will only take us back maybe 50 years, to what we had when I was a boy.
We really need to be aiming much higher and approximating the levels of biodiversity we see every summer when we take people to our 'secret corner' of Poland.
I dare you to come with me and open your eyes to the massive losses to our wildlife in the UK. Only then can you see what we've lost and how we can get it back.