Japanese knotweed cannot be cured, a major study which tried 19 methods over three years has found.

Researchers from Swansea University conducted the world's biggest ever study into eradicating the invasive weed at two sites in Taff's Well, near Cardiff, and in Swansea.

But despite using various chemical solutions, physical projects and a mixture of the two, the scientists found no definite ways of killing the plant completely using current methods.

Professor Dan Eastwood from the project said: "Basically, we're discovering how best to tackle invasive plants in real world conditions, informed by evidence of what actually works. We began focusing on knotweed at a time when there was a great deal of hysteria surrounding it.

"At the time, most information for people affected by the plant was largely based on anecdote. This led to the prospect of unscrupulous companies offering expensive and ineffective treatment solutions.

"It was incredible to us that there was no long-term, large-scale field trial analysis of the treatment methods used to control Japanese knotweed."