Giant hogweed has been discovered on the Great Ouse in Brackley, where the river passes under Buckingham Road, west of the A43 Brackley bypass.

The plant's stem and leaf stalks contain a sap which is released by handling, cutting or just brushing against the plant. This sap contains furanocoumarins, which make the skin hyper-sensitive to the sun and cause painful blistering.

Eric Roberts, the retired writer of the Chronicle & Echo's Country Diary column, said the plant, which is also known as cow parsley, first came to Britain more than 100 years ago, from the Russian Caucuses on the Orient Express.

He said: "I haven't seen it for years, but whenever I have seen it I have warned people to steer well clear of it.

"It is a strange plant, though. A long time ago, before my time, youngsters always used to use the smaller stems as pea shooters. That always puzzled me though; surely those youngsters would have ended up with dreadful blisters?"

Hogweed is easily recognisable as it grows up to 5m tall, has a large, umbrella-like flower head with white flowers and a green or brown stem with dark red or purple spots or blotches.

South Northamptonshire Council has warned people against touching the plant and has said anyone who does touch it should immediately seek medical attention and seal the affected area with clothing.

The council's environmental protection team are investigating the sighting and are advising owners of the land affected on how it should be removed.

For more information, contact the council's environmental protection team on 01327 322314, or send an email to environmental.protection@southnorthants.gov.uk