Make sure you understand the law before tackling Japanese Knotweed.
If you cause the Knotweed to be spread off-site, you could find yourself at the wrong end of criminal proceedings under either the Wildlife and Countryside Act 1981, or the Environmental Protection Act 1990 “duty of care”.
Offences under these Acts can even result in custodial sentences. If you consign Knotweed infested soils off site other than strictly in accordance with these legislative requirements, whether intentionally or not, you will run the risk of prosecution.