Lawyers have hailed a Court of Appeal ruling on Japanese knotweed as a victory for homeowners.
Three leading judges ruled in favour of two householders whose properties had been affected by the hazardous plant.
Stephen Williams and Robin Waistell, who own two adjoining bungalows in Llwydarth Road, Maesteg, South Wales, were awarded about £15,000 in damages at Cardiff County Court in February last year after they sued Network Rail - which owns the land immediately behind their properties.
The pair successfully claimed that, while there was no actual physical damage to their properties, the hazardous plant had encroached on their land and reduced the value of their homes.
Network Rail challenged the ruling at a hearing in June, but it was upheld by the Court of Appeal on Tuesday.
The court found the neighbours were entitled to compensation for their "diminished ability to enjoy the amenity and utility of their respective properties".
Speaking after the ruling, Samantha Towle of JMP Solicitors - which represented Mr Williams, said: "This is a fantastic result for not only my client Mr Williams, but for other homeowners in a similar position of which we represent many around the country."
Ms Towle said the result of the ruling is that both men will keep all of their damages - including the damages they are entitled to for the fall in the value of their properties.
Rodger Burnett, of Charles Lyndon law firm - which represented Mr Waistell, said: "This is a great result for Mr Waistell and homeowners up and down the country.
"For far too long landowners like Network Rail have paid scant regard to the impact that their failure to adequately treat Japanese knotweed has had on adjoining properties.
"Hopefully now organisations like Network Rail will take their responsibilities seriously and remove the knotweed on their properties."
The bamboo-like plant, which grows quickly and strongly and spreads through its underground roots, can undermine the structural integrity of buildings and is expensive to treat.
The county court judge found that, although there was no actual physical damage to either man's property, the knotweed rhizomes had extended under each of their bungalows.
Stems of knotweed behind Mr Williams's home sometimes knocked against his windows and had "blighted" his property, the judge concluded.
He said Network Rail's efforts to treat the "pernicious weed" following the homeowners' complaints in 2013 were "not adequate or reasonable".
Mr Williams said: "I'm really happy we have eventually won.
"It has been a long hard battle, but there is basically a light at the end of the tunnel now."
Japanese knotweed has been present on Network Rail's land at that location for at least 50 years.
Announcing the Court of Appeal's decision, Master of the Rolls Sir Terence Etherton said: "Japanese knotweed, and its roots and rhizomes, does not merely carry the risk of future physical damage to buildings, structures and installations on the land.
"Its presence imposes an immediate burden on landowners who face an increased difficulty in their ability to develop, and in the cost of developing, their land, should they wish to do so, because of the difficulties and expense of eradicating Japanese knotweed from affected land.
"In this way, Japanese knotweed can fairly be described as a natural hazard which affects landowners' ability fully to use and enjoy their property and, in doing so, interferes with the land's amenity value."
The court refused to give Network Rail permission to challenge the ruling in the Supreme Court.
A Network Rail spokesman said: "As many gardeners know, Japanese knotweed is invasive and requires several years of treatment to remove.
"Once identified, Japanese knotweed growing on our land is entered into a treatment programme.
"We will continue with this established regime, which complies with legislation and helps us run a safe, reliable railway.
"Network Rail is aware of today's ruling by the Court of Appeal and is considering its implications."