Japanese knotweed – also known as Fallopia japonica – is an invasive, non-native plant.
You are not legally obliged to remove Japanese knotweed from your land or to control the plant.
However, if you allow Japanese knotweed to grow onto other people’s property you could be prosecuted for causing a private nuisance.
It is an offence under the Wildlife and Countryside Act 1981 to “plant or otherwise cause Japanese knotweed to grow in the wild”. It is also an offence to dispose of Japanese knotweed material in green or general waste bins.
You can find more information about Japanese knotweed and other harmful weeds here.