The Environment Agency has described a cyanide spill into a West Midlands canal as “unacceptable” and promised robust action if any wrongdoing is found to have occurred.

A major incident was declared after the spill of sodium cyanide into a canal in Walsall on Monday. The public have been advised to avoid about 12 miles of canals and towpaths in the area and on Thursday a UK waterways boss described the situation as “distressing” and “infuriating”.

The Environment Agency said it was investigating a metal finishing company, Anochrome Ltd, after the spill.