Ring rot can devastate potato crops but is harmless to humans

The farms - all in England - were supplied with the same species of potato as the farm at the centre of the outbreak in Wales.

Experts have warned the first outbreak ever to hit the UK could cause spiralling prices and ruin farmers.

The investigations are a precautionary measure to prevent further spread of the highly infectious bacteria.

The three affected farms, one in the north of England and two in the south, all received seed potatoes of the same variety as those in the original outbreak.

This new information merely means that we get the opportunity to make checks - it does not mean that the disease has spread Department for the Environment, Food and Rural Affairs

These potatoes were not from the same Dutch farm as the original batch.

The Department of the Environment, Food and Rural Affairs (Defra) said it was seeking information from the Netherlands about other types of potato delivered from the source farm.

A Defra spokesperson also stressed that no evidence of the disease had yet been found.

"This new information merely means that we get the opportunity to make checks - it does not mean that the disease has spread."

All the relevant batches of potato are being held for testing, but other business on the farms is continuing as normal.

Potato ring rot is a disease which is widespread in crops across Europe, having been identified in recent years in France, the Netherlands and Denmark.

The disease appears as black rings within the potato and the vegetable rots.