Sarah BrealeyA huge increase in numbers of exotic deer is threatening native wildlife, experts have warned. Muntjac deer were introduced to East Anglia in the 19th century but have now spread throughout the region, especially Thetford Forest.Sarah Brealey

A huge increase in numbers of exotic deer is threatening native wildlife, experts have warned.

Muntjac deer were introduced to East Anglia in the 19th century but have now spread throughout the region, especially Thetford Forest. There are 150,000 muntjac deer in the country which feed off wild flowers and young shoots of trees, such as saplings and coppice growth, which can damage or even destroy woodland.

Emma Goldberg, from Natural England, said: 'You either have to fence deer out, which is expensive and high maintenance. Or the thing no-one wants to talk about, controlling deer through shooting them.

'We have to really make a hard choice here. Do we like to see deer so much that we don't want to see the birds, the butterflies and the dormice, living in their natural habitat? That's the choice we're facing.

'You have to remember that plant species support a host of animal species. So within thickets you can find dormice, the nectar of the bramble and flowers are really good for butterflies and ground nesting birds like nightingales. Once the deer have eaten all that shrub layer out they've got nowhere to live.'

On Monday a BBC Inside Out programme will highlight some of the problems caused by deer.

Suffolk Wildlife Trust has previously complained that muntjac have a 'serious impact' on woodland ecology by grazing on tree shoots and eating bluebell and oxlip flowers.

Norma Chapman, from Barton Mills, near Thetford, is a leading authority on muntjac. She said: 'They're absolutely fascinating animals, they've adapted so well from subtropical dense forest in Asia to our climate, our vegetation.

'All other deer in Britain have seasons. A healthy doe muntjac has the potential to produce a new fawn at seven-monthly intervals, and as long as she doesn't get run over or caught by a dog, she has the potential to live into teenage years.'

Many of East Anglia's muntjac are thought to have descended from deer introduced by the 11th Duke of Bedford, who built up a deer collection at Woburn Abbey in Bedfordshire in the 1890s. Some escaped and some were released into the wild.

The Norfolk Broads also supports a smaller population of Chinese water deer, which could depend on their new habitat for survival. These deer are thought to have escaped from Woburn during the second world war, when troops were billeted at the abbey.

Arnold Cooke, who has studied them, believes the water deer should be encouraged because they are not as invasive as muntjac and they are endangered in their native country. 'On a world scale, they are officially classified as vulnerable because there are relatively few of them left in China. Here in England, we've got something like 30pc of the world's population.'

t Inside Out is on Monday at 7.30pm on BBC One.