Plans outlined to tackle knotweed

The invasive plant can even grow through concrete and tarmac

New guidelines are being prepared for property developers to help them deal with knotweed, the Environment Agency has revealed.

Japanese Knotweed, a particularly invasive species, can kill other plants and grows through concrete and tarmac to damage pavements and buildings.

The Environment Agency said the "unbelievably strong" plant caused concern and had to be controlled.

It is illegal to grow knotweed in the wild and offenders can be imprisoned.

Alistair Driver, the agency's national conservation manager, said: "It's unbelievably strong. It can actually grow through concrete and through brick walls.

Olympic threat

"I've actually seen pictures of it growing through tarmac and pavements. And that's a really serious problem in some parts of the country, like for example, the Swansea area and down in Cornwall."

Flourishing in any soil - however poor - Japanese Knotweed spreads relentlessly, overwhelming other plants and damaging ecosystems.

Experts say a new plant can grow from a piece of root the size of a garden pea.

Billion-pound cost

The Victorians introduced the plant to the UK from Japan but many dug it up and threw it out.

It then spread in the wild after starting to overtake gardens.

The problem is now so great the government has estimated that controlling the weed countrywide would cost £1.56bn.

And the removal of knotweed from the 2012 Olympic site in east London could cost hundreds of thousands of pounds.

Planting it or dumping it can lead to two years in prison, a large fine, or both, under the Wildlife and Countryside Act 1981.