Homeowners on alert for alien invader

IT was first brought to Scotland by wealthy Victorians looking for an attractive and exotic plant to brighten up their gardens.

• Japanese knotweed: invasive and very expensive to eradicate

Now homeowners whose properties are blighted with Japanese knotweed are finding it difficult to sell their houses - as banks are refusing to offer mortgages on contaminated plots.

Eradicating the invasive plant, which grows rapidly and can push through cracks in concrete, can cost thousands of pounds and weeks of disruption for householders.

Hundreds of homes are believed to be affected as the plant is now present in all areas of Scotland, except Orkney. Sites on which new homes have been built are particularly affected, as the plant's spores spread through being transported on building equipment and along waterways.

Specialists in knotweed eradication say they are dealing with an average of 15 calls a week from anxious homeowners in Scotland who fear that the weed is making their properties almost unsellable.

Virtually all the main lending banks, including RBS, Bank of Scotland and Santander, are unwilling to provide mortgages if a surveyor's report has any hint of knotweed contamination of a property.

One banking source said: "In the world of mortgage lending, if the dreaded words Japanese knotweed are mentioned, the phone is practically slammed down immediately. It is something everyone is quite concerned about."

Musketeers Group, a contracting firm involved in knotweed eradication, said the number of calls from homeowners to its Glasgow office had gone up significantly in the last six to eight months.

"At the moment, we are only scratching the surface of the problem - but we believe there is a lot of misinformation around about the plant," said managing director Maxime Jay.

"Banks are refusing to provide lending to properties with Japanese knotweed and we think they need to change their policy. The guidelines wrongly assume that knotweed can grow through concrete."

In its native Japan knotweed is controlled naturally by insects and fungus. But in Britain it has now become the most invasive, alien species currently spreading around the country. It grows quickly if left untreated, up to 10cm a day, and, by late summer, produces a lush green bush, more than two metres in height, with bamboo-like stems and heart-shaped leaves.If unchecked, its long roots and shoots can damage building foundations. In 2007, Waterfront Edinburgh, which is involved in building thousands of homes on former industrial land on the shores of the Firth of Forth, had to start a three-year, 80,000 eradication programme when it discovered knotweed on part of the site.

The Royal Institute of Chartered Surveyors Scotland (RICS) says if the plant is picked up by a survey it is best to get a regulated licensed contractor to deal with it.After chemical treatment, the remains, classed as hazardous waste, must be bagged up and taken to a landfill site.

Sarah Spiers, deputy director of RICS, said surveyors were bound to report evidence of knotweed. "It is something which has been designated as on a 'contamination' list," she explained. "It depends on how serious the problem is, but people are unlikely to find it easy to secure a mortgage on a property like that."

Under environmental law policed by Scottish Natural Heritage, it is illegal now to plant knotweed but the Japanese Knotweed Alliance said it can be spread by vehicles, footwear and watercourses.

It is thought to have thrived during the pre-recession, when developers spread it from site to site on equipment and shoes.

"This is an issue we are aware of, but it is a matter for individual lenders and the amount of caution they wish to exercise," said a spokeswoman for the Council of Mortgage Lenders.