Firefighters were drafted in from around the county to try to clean up the highly-toxic formic acid, which can give off dangerous vapours and can cause severe chemical burns and eye damage.

The leak, from a 1,000-litre container on the back of a lorry, was first spotted by a warehouse worker when the HGV was parked at the Dachser Transport Ltd site, in Gowerton Road, in Brackmills industrial estate.

A spokeswoman for Dachser confirmed a male lorry driver, believed to be in his mid-40s, was taken to hospital to test whether or not he had been exposed to the acid.

She said: "It was a purely precautionary measure, and he was back at work within an hour. The liquid was formic acid, which is found naturally in ant bites.

"The leak was only a small amount but the fire service was called to help absorb it, and then the waste was transported back into containers according to safety guidelines and regulations.

"The incident will be investigated because it was a chemical leak. The trailer itself was provided by P&O, who were delivering goods to us through a sub-contractor, so it wasn't actually any equipment from Dachser that was involved."

A spokesman for Northamptonshire Fire and Rescue confirmed crews were called to the scene of the leak shortly before 8am yesterday and spent more than three hours cleaning up the spillage and absorbing the acid.

He said: "The hazardous liquid was absorbed with five tonnes of sand. Because this was a chemical incident we had to decontaminate our firefighters, who wore gas-type suits.

"We had specialist crews from Wellingborough and Rushden, as well as crews from Mereway, The Mounts and Moulton in attendance."

Formic acid, which is secreted naturally by bees and ants, can cause serious health problems if the skin comes into contact with it, or if concentrated vapours are breathed in. It is mainly used as an antibacterial agent in livestock food.

P&O was unavailable for comment yesterday.