Londoners were today warned to prepare for a “surge” in destructive Japanese knotweed after the wettest and warmest winter on record.
The feared weed, which usually appears around May, has already been spotted sprouting across the capital.
Described by the Environment Agency as “the UK’s most aggressive and destructive invasive plant”, it can damage foundations, grow through patios, drives and floors, bring down boundary walls and block drains. It can spread up to 10cm a day and has been known to resist poison and fire.
Houses have plummeted in value due to its presence, and some lenders have refused to grant mortgages because of it. Environmental scientist Nic Seal, founder of knotweed removal firm Environet, urged people to be “vigilant”, saying: “We have found knotweed across London already.
“Normally we’d see it picking up in late April, May. It’s because we have had a lot of rain recently and it’s been fairly warm. It’s not fussy in where it grows and anyone is at risk. We can expect a surge across London this year.”
Mr Seal said the banning of pesticide Tordon — used until it was proved to damage other plants and trees — may be a problem: “Tordon is aggressive. Other chemicals will make knotweed look dead but won’t kill it. So in a couple of years we might see another spike.”
He said he was aware of properties that had lost 25 per cent of their value because of the plant, and cases of buyers suing home sellers for not declaring knotweed on conveyancing forms.
Last December was the warmest on record, with Met Office data showing a UK average temperature of 7.9C, 4.1C higher than the long-term average.
Knotweed was introduced in the 19th century as an ornamental plant but it is now illegal to spread it. The Government has estimated eradication would cost £1.5 billion. An infestation plagued Hampstead near the homes of Thierry Henry, Tom Conti and Esther Rantzen.
Two years ago Matthew Jones and Sue Banks demolished their property in Broxbourne, Hertfordshire, “because of knotweed”. In 2013 Kenneth McRae, 52, beat his wife Jane to death then killed himself, leaving a note saying he was “driven to madness” by knotweed near their West Midlands home.