The bacteria can survive the pasteurisation process

Some experts have suggested that this type of bacteria is associated with Crohn's disease.

Crohn's is an inflammatory bowel disorder affecting around 150,000 people in the UK.

The government is expected to issue guidance outlining measures to stop the spread of the bacteria in June.

We will be giving out fresh guidance to farmers and also to local vets and animal health officers in June Department for the Environment, Food and Rural Affairs

Symptoms include diarrhoea, abdominal pain, weight loss and fatigue.

One expert has suggested around 90% of patients with Crohn's have the bacteria - mycobacterium avium paratuberculosis (MAP) - in their gut.

Professor John Hermon-Taylor at St George's Medical School, says he has "unequivocal evidence" that the bacteria is found in the majority of people who have Crohn's and a minority of people who do not.

Stop the spread

MAP is known to cause a similar, chronic infection of the gut in cattle called Johne's disease.

Around 17% of herds are thought to contain infected animals.

The government says the link between MAP and Crohn's has not been proven.

But the Department of the Environment, Food and Rural Affairs (Defra) is set to introduce precautionary measures to stop the bacteria spreading to humans.

It will tell farmers to screen for Johne's, to prevent infection through contaminated watercourses and pastures and to protect young calves who may catch the disease from their mothers.

Johne's can be difficult to spot as it can be years before an infected cow shows signs of the disease.