LURKING behind the bushes along the Thames towpath in Richmond lurks a dark intruder which threatens to beat your primrose to a pulp, slay your sunflowers and massacre your marigolds.

It is actually incorrect to call it an intruder since the Japanese Knotweed was introduced to this country as a ornamental plant, back in the mid-nineteenth century. Since then it has become a serious problem in a range of habitats, particularly roadsides; riverbanks and derelict land, by causing structural damage.

This persistent perennial, which can grow to a height of 3 metres, with bamboo stems, arching branches and clusters of creamy white flowers, prevents native seeds from germinating to eventually form its own single crop.

The main concern comes from the weed’s resilience and extensive roots which burrow deep into its surrounding area, growing at least half a mile from water and taking up to three years to kill.

A stark warning to Richmond’s borough comes from Swansea, where an estimated 620,000 tonnes of Japanese Knotweed covers the region.

Swansea City Council failed to deal with the weed when it grew on the Gower Peninsula, now they estimate that it would cost more than £10 million to eradicate. The area is now one of the most infected places in the world to be infested by a plant.

In 1981, The Wildlife and Countryside Act made it illegal to spread Japanese Knotweed however flytipping garden waste and moving contaminated soil has ensured its survival.

Ann Temple is a retired biologist who is undertaking a community project to map the weed in the borough in the hope the council will find the funds to eradicate the plant.

She said: "I applied and received a Millennium Award and decided to address this issue.

“The first step is to map out the areas in the borough where the plant exists, hopefully then the council will be able to fund a full spraying regime."

A spokesman for Richmond Council said: "The council monitors the plant, but resources prevent full control, for which repeated treatment with a translocated herbicide is recommended.

“The estimated cost of eradicating the weed from the borough would be likely to be over £100,000."