JOHN YANG: Beavers were hunted into extinction in England in the 17th century.

This past week, for the first time, beavers were legally released into the English countryside.

Conservationists hailed it as a watershed moment for this keystone species, which helps combat flooding and drought by engineering the landscape with dams and channels.

Alex Thomson of Independent Television News was at Purbeck Nature Reserve in Dorset for the historic event.

ALEX THOMSON (voice-over): The sea mist wreathed Corfe Castle from dawn, but the way is now cleared for beavers here and beyond.

A short walk to the edge of the ponds in the National Trustús Purbeck Reserve.

X literally marks the spot so many have worked so long to achieve.

HARRY BOWELL, National Trust: Why is that exciting?

For someone like me, who spent 40 years working to restore nature, today marks something really exciting, which sounds like a small thing, which is two pairs of beavers being released here at Purbeck.

That actually is a big, bold step in reversing the decline of beavers.

ALEX THOMSON (voice-over): All but cut off from the mainland, Purbeckús a stunning landscape of lagoon bog forest.

At the designated release spot, the cordon is up.

They are ready.

Final preparations.

Remote cameras in place.

And they arrive.

Two beavers driven overnight from Tayside, nine hours north.

Bang on time.

The crates are set down.

They emerge a little stressed, hesitant even.

This the first of many legal releases after a 400 year absence as these animals were hunted to extinction for their fur, meat and even scent glands.

MARY CREAGH, Minister of Nature: Itús a really historic day for nature in this country to see the first wild beaver release is a really important step in nature recovery.

ALEX THOMSON (voice-over): Not everyone is convinced.

The NFU skeptical, verging on hostile to government sponsored reintroduction across England.

DAVID EXWOOD, National Farmersú Union, Deputy President: Thereús just not a realistic option there for farmers to be able to manage the impact for beavers.

There will be cases where they need to remove beavers.

There will be places where our members will not want to see them.

And we just donút think that is there in his current plan.

ALEX THOMSON (voice-over): But the government insisted today robust impact management is in place.

MARY CREAGH: There will be capital grants available to deal with any beaver impacts, including the ability to remove beaver dams within two weeks of their construction should they pose a risk to crops and also in extremists to use lethal control.

ALEX THOMSON (voice-over): Spring hedge planting this morning.

Local farmer Ian Baggs is, well, constructively skeptical.

It could work, it should work, but it needs more government support.

IAN BAGGS, Dairy Farmer: So the challenge weúve got is that thereús lots of benefits and thereús a positive story here, but thereús also risks.

And the benefits are societal.

The risks are to individual small businesses.

ALEX THOMSON: Farmers.

IAN BAGGS: Including farmers and potentially other landowners, people who live in houses that are subject to flooding.

ALEX THOMSON (voice-over): Beavers, of course, create dams which filter river water, purifying it.

Their ponds bring hosts of insects and thus birds and reptiles.

That water protects river systems from both droughts and floods.

But Purbeckús idyllic nature reserve is the easy bit, studded with heath, forest, lakes and no farming.

ALEX THOMSON: So where do we go from here?

Well, the rather messy reality is that the beavers will breed and theyúll breed a lot from this and other sites and theyúll spread out across England and down the line, will arrive at a balance, perhaps uncomfortable, where in some areas theyúll be cherished and will thrive and will be loved.

In other areas, frankly, theyúre going to get moved or theyúll be shot, legally or illegally.

That might sound brutal, but ultimately we will have replaced a key species, a missing piece of our biodiversity jigsaw after centuries.

And that surely is progress.

ALEX THOMSON (voice-over): So todayús legal release joins what are known as beaver bombings, the illegal release of animals already thriving in England.

Hundreds of them achieving the right balance in all this will take time, but the official beginnings of that started today.

JOHN YANG: Thatús Alex Thomson of Independent Television News.