A tiny insect is being released into the UK to help the battle Japanese knotweed, scourge of construction sites up and down the land.

The weed costs more than £150m a year to control and clear, according to wildlife minister Huw Irranca-Davies.

Now, a natural predator of the weed from Japan is being released on a trial basis in the UK.

The bug, Aphalara Itadori, has already undergone laboratory tests which suggest it would not harm any other UK species, including closely-related plants and important crops.

The bugs, which grow to only 2mm to 2.5mm, will be released at two sites initially, under close supervision.

If these outdoor trials are a success the trials will be extended to another six sites.